They probably had to rewrite it from scratch every time a new platform came out.
And then rushed to finish it before the Xbox 720, PS4 or whatever is next. There's no excuse for spending that long though, considering the resources they must have been able to throw at it.
( drimble he'd been white, he'd been black, Mon 20 Jun 2011, 19:07, archived)

That's no excuse for using the same aliens and weapons as duke 3d

( CowJam, Mon 20 Jun 2011, 19:18, archived)

What happened was 3D Realms acted like a teenager who hadn't done their homework for about 12 years
until they all got shitcanned, then 2K and Gearbox came along and made a right fucking hash of it, which they then ported over to the Xbox, badly.
( BraynDedd Natasha Kaplinsky's labia majora, Mon 20 Jun 2011, 19:20, archived)

Quote taken directly from the back-of-box copy

( drimble he'd been white, he'd been black, Mon 20 Jun 2011, 19:29, archived)