These 1000s of pages for bills began when Congress itself stopped writing legislation and the special interests began writing it. Its been decades since Congress has written law themselves.

The special interests write bills that benefit themselves. They shop it around to legislators who can be bribed to sponsor said bill. The leadership and the whips then intimidate the legislators into voting for the bill. It may get some edits to make part of it palatable to the public while hiding its true intent.

Its this process that drives Pelosi to say you have to pass the bill to know whats in it.