Congress is hopelessly broken, gridlocked and unable to pass policy on its own merit. That's how we end up with quadrillion page omnibus bills every year. It's a failed institution, and it's been this way since at least Reagan.

The process itself must serve evil. As a process, single issue bills permit a clear stand on good/evil with debate on the issue to convince/justify vote. Multi issue bills permit a horse trade of my evil interests to be included for your evil interest to also be included.

It can backfire though. Too big a deal can get some to leave the corruption consensus over 1 provision included. Everyone is given more power to grandstand against evil.