No idea either lol I still don't know why the levels are different at all. THUG2R released in January or March of 2005 while THAW released in October of 2005. By those measurements, Neversoft should've been sent the completed level source files for compiling them into THAW formats. The only reasons I can come up with are:
1. They were sent early, incomplete versions either early on in THAW's development or later on due to some file mix up and it was too late to fix. Makes some sense, considering Casino in particular is a story level so they would need it kind of early on, perhaps even in an unfinished state. And what is an elevator and tiny upper room to normal players? Only those of us still playing the games in 2016 are probably obsessed enough to know these changes lol
2. Memory allocation in THAW meant they needed to cut parts of the levels because it was the quickest way to solve the issue. But I'm skeptical of this because, sure, the level textures are better in THAW, but the poly count looks the same. Going from PSP to PS2 is such a considerable leap too.
Either way, my ideas just play off my other feeling which is that THAW was super rushed and tried to do too much in too little time. And I think I've heard others thought the same.
