Part of what makes repeating so hard is, it's hard for teams who won it all to stay engaged the following season and it's easy to develop some bad habits or "laziness"
Look at Denver. People thought that team and Jokic could repeat easily and build a dynasty, yet they went out in the 2nd round last year and even this year look great, not elite though.
Same with Giannis and the Bucks in 2021, since then they haven't been back