My ex-husband was an agnostic Jew and as he put it, "We Jews are not so much into the emphasis on heaven or hell." That is true and he is correct, although the lack of detail mention of heaven or hell in the Old Testament is not reflective of both their reality and their inevitability.
What people need to remember is that the books of the Old Testament were written while God was physically present with the Patriarchs and the Israelites. God did not "have to" provide Israelites with a lot of "after life" information because he was right there with them telling them what to do! The vast majority of the Old Testament is written faith history (events) and instructions about how to worship God and have pious lives. All the people had to do was actually obey God as he instructed them both directly and through the priests and prophets and they were going to "end up in the right place," if you get my drift.
You can contrast this with pagan works such as the Egyptian Book of the Dead. The ancient Egyptians had no clue regarding direct experience with God or the true nature of the after life, so they made up a huge pantheon of gods and goddesses (like the early Romans and Greeks) AND they developed what can only be described as an obsessive compulsive "cook book" for "guaranteeing" that those rich enough to perform all the rituals and requirements would "end up in the most advantageous conditions." I say cook book because they imagined quite literal activities such as upon death their organs being weighed by gods to determine virtue and so forth. So people who do not have God in an active presence such as had the Israelites often obsessed quite a bit about the after life.
In contrast, God's "chosen people," the Israelites, were instructed by God in the two fundamentals of ensuring "a good outcome." The first was the system by which they know, acknowledge and worship God, and thus always know precisely their place in his heart and in the spiritual order as a whole. The second was the commandments and laws by which they should live honorable and virtuous lives that would ensure successful living, prosperity and also avoid sin. Wisdom and praise were outputs of those two fundamental systems. That is why the Old Testament really did not focus on "what it's like on the other side" because they had God BY their side while living (and as you can read, it was a struggle to get them to obey God and avoid sin even as God was right there with them).
When Jesus Christ as Messiah and Savior performed his public ministry, that became the time when frank talk about both heaven and hell were needed. This was for several obvious reasons. One is that Jesus was bringing to the faithful God in a form that he had not yet appeared, which is the physical reality of how God as the Son of Man can dwell and speak to "fellow humans" incarnated in a human body. Therefore Jesus had a platform by which to first instruct in words and then demonstrate with his own body what happens when a person dies and is received by God in judgment. The second reason is that with the New Covenant Jesus had to make very clear to the faithful what the rewards of obedience and the consequences of sin and disbelief would be not only in life but upon death. This is because in foreseeing of the destruction of the Temple and dispersal of the chosen people a new "church" was needed that dwelled in the hearts of all people so that they would have the road map by which to live and achieve both personal and community salvation. The third reason is that while Jesus preached specifically to the Jews, many more than Jews listened to him and the Apostles were instructed to take the faith to the entire world, "the Gentiles." Thus people from all backgrounds and cultures had to have a clear understanding of what happened to each human after death. The fourth reason is that Jesus through his teachings, admonitions and parables often described the wages of sin and where someone would end up (hell) if they lived a sinful life (he even describes a person in hell asking for permission, and not receiving it, for warning his sinful brothers who are still alive about the reality of hell). Jesus also is very graphic in his warning that it is better to deprive one's self of offending and sinful body parts than to risk hell as a consequence of their action, and likewise of the consequences of hell to those who lead children into sin.
A fifth reason that Jesus described heaven and hell in more detail than in the books of the Old Testament is that as Jesus described, he is treating them as friends and not as servants. Hence, friends are entitled to know the plans and reasons for what will happen, and this includes God's still unrevealed timing of the end of the world and the resurrection of the body. God revealed as much as he did through Jesus in honor of the shifting relationship where God expects humans to be knowledgeable co-operators in their own salvation. Unlike Adam and Eve who rejected earthly paradise, only the "saved" will be part of the new world in their resurrected bodies. In other words, God is treating the faithful as friends in addition to children who are constantly tempted to sin, and God lets humans know that there will be a New Kingdom with a bodily reality at some point in the future. Thus humans are, to use a modern business term, directly invited to be knowledgeable investors in not only their own personal salvation and reward in heaven but also eligible participants when it is the End of Days and the old world passes away into the new.
The sixth reason is that human nature being as it is, society tends to become depraved and fall apart the instant humans lose sight of the reality of unbearable and eternal hell. I wish that were not true but it is what it is, and you can see that today everywhere you look. Jesus did people a favor by being a stern in his warning as he was, and soft shoeing the reality of hell is not a favor, as we can see today. Humans need to be reminded of the reality of fire and brimstone. This, incidentally, is why in the revealed book of the Qur'an over six hundred years after Jesus died and resurrected there is such vivid emphasis on the eternal punishment in hell for sinners and willful disbelievers. God is fair, just and merciful; he does not miss a chance to tell humans the truth and to try to induce as many as possible to be believing, faithful and virtuous.
I hope you have found this to be helpful.