I would say that most hallmark results in theory-heavy mathematics (number theory, algebraic geometry, topology, …) could stretch to at least a book length trea

I would say that most hallmark results in theory-heavy mathematics (number theory, algebraic geometry, topology, …) could stretch to at least a book length treatment if you wanted a mostly self-contained proof. It sounds like the main difference with this theorem is that the writeup of the original proof was so complicated, terse, and error-prone, that very few experts even understood it.