It probably should be an independent bill. Each reasonable sub-section of the process should be it's own bill.
But as a horridly complex mess each and every Congresscritter or Senator can use various parts of it to their advantage. They can vote for it and tell unhappy voters they voted for it because most of it was pretty good and they can fix the problems later. Likewise they can vote against it and tell folks there were parts that were so bad the good parts weren't worth it. And as small simple parts, thjey can't vote either way without hurting themselves, hence no easy way for us.
Heck they could tie up a "fence" bill for a years. How high, how wide, where it goes, where it stops, what equipment, how far from the border can it actually be, etc etc etc ad infintum, ad nauseum.