Mike, that's been being talked about for 30 years and I don't know what the hold up is, but I can guess.

It's not hard to figure out. You just saw it with the Steve Bannon/Laura Loomer broadside against H-1B visas (joined by Bernie Sanders).

There's a part of the GOP base that's against letting people from other countries come here to work - that insist that the American economy should be reserved solely for American citizens, not foreigners. There's also part of the Democratic base that's still deeply concerned about the economic impacts of what they see as an exploitative labor relationship (the Democratic side got squelched a little bit during the ascension of immigrant activists within the progressive coalition - but they're still out there).

That's enough to kill a guest worker program. There's enough opposition to make this a bit of a lift. Also, since it's mostly perceived by both sides as helping the industries that employ these workers rather than anyone else, neither party wants it enough to just do it as a standalone; they want to fold it into a larger bill, and use it as coalition bait to get some powerful domestic groups (especially farmers) to support their other priorities.