It just takes longer when the people you’re dealing with are insane Leftists.
In his first two years perhaps he could have negotiated and got more wall built. But Trump did not build a coalition for his wall. He is a CEO type and not a politician. The things that everyone loves about him (non-politician) can also be his weaknesses. It takes teams to win and Trump is a team of one and maybe a few more.
Now? Not happening. It comes down to votes. Trump just doesn’t have them.
He may as well issue an executive order if he wants something done on the wall.