It's called "bloat", a441. Nowadays, developers simply don't worry about keeping filesize small. Since hard drives are insanely large and broadband is common, they just don't worry about it anymore. Most commercial games take up over a gigabyte now. I personally don't care much, since after all, if they take less time to make it small, they can spend that time doing other things or releasing the game early. The only bad thing about it is for downloads and for small hard drives.
Do note, though: Most commercial games support mods, a441. The reason is obvious: Counterstrike. Counterstrike kept Half-Life alive and well years after its release, and is still alive today. Considering Half-Life is over 5 years old, that's pretty damn impressive. A developer nowadays would have to be insane not to support mods of some nature in a new release.