The 2017 TCJA was passed on pure party line votes (in the House, all Democrats and 12 Republicans opposed the bill), so it definitely wasn't bipartisan. More generally, big tax cut (the top 0.1% saw about $250K in lower taxes under the TCJA) and big spending bills jam in all sorts of random shenanigans to try and prove themselves revenue neutral, even though they almost never work out as described. One favored tactic, as we see here, is to kick big cans down the road and let a future Congress work out the problems. They (and this is one of those cases where both parties are equally complicit) know what they're doing, they just don't want to be honest about the fiscal implications of what they're doing.

Fixing these tax issues, on the other hand, would have had to be attached to the NDAA or omni last session, both of which require bipartisan support; big bipartisan bills are so contentious that it's hard to get unrelated deals through, especially since everything goes down to the wire these days. In this case, a deal that would have expanded child tax credits in exchange for a bunch of corporate and high net-worth household goodies, including section 174 fixes, was on the table, but couldn't get through negotiations. (I'll note that, while the Republicans created the section 174 mess in the first place, they are now trying to repeal that and other TCJA changes, but aren't willing to add lower-income individual tax cuts into the mix, which is what stalled things in the last Congress.)

It's a hell of a mess, and things are made crazier by the weird power dynamics in the current House leadership, where a small group of fiscal bomb-throwers have outsized power in the Republican party (and it's not clear that they care about tax minutiae, at least not while they're playing with a federal default on the national debt), but the inter-party margins are so slim that you could potentially cobble together a bipartisan majority on the edges. No one seems to like the section 174 situation, so it's at least theoretically possible that you could get a small coalition together to cut a deal at the last minute -- but I'm not sure we can count on that.