Minecraft stopped being a game of exploration to us, which is why we liked it. We went to it to discover, like we have with many games before it, yet we became enthralled in the game behind the exploration. We have since discovered all there is to know about minecraft, we know how to dig sand, we know how to efficiently acquire resources, and we know how to cheat the system. We're nostalgic for old minecraft because old minecraft was a fresh experience, not because it was better. The minecraft experience is the same for someone today as it was for us back when we began.
Also most of the new terrain is bland, because they replaced interesting terrain with habitual terrain. Enabling easier building of large structures but a less interesting landscape to explore.