Rollercoaster Tycoon was the last of an era, not a sudden burst of genius.
Before Doom (1993), almost all games were assembly. Doom was a shock to the industry. You could now write a high performance, multiplatform, sophisticated game in a compiled language (C). When I say multiplatform, I don't just mean how it was ported to everything later. It was developed on NextStations first. DOS was the first port. So it proved all of the above immediately on release.
We take for granted that C is performant now, but that wasn't obvious until optimizing compilers got good and someone tried.
Rollercoaster Tycoon (1999) is the last notable title that used ASM. It's impressive in many ways, but it wasn't as much of a standout as it seems now. Six years earlier to its release, that was just how games were done.
It's notable that the only port of Rollercoaster Tycoon was the original Xbox, which was also x86. Nobody wants to rewrite it for anything else.