There's an important distinction to be made between what happened with the ACA and what happened with the current tax bill. It was bipartisan because republicans at all stages were given the opportunity to engage, plus a lot of the basic foundations of the ACA were praised by conservative economists and it was directly based off of Romney's healthcare plan. At no point were republicans shut out or their opportunity to amend the bill taken away. Many republicans even supported the individual mandate before the ACA came along!

With the republican tax bill, democrats were outright denied any opportunities to work with republicans. They were shut out of the entire process, all of their amendments were denied and there was no opportunity for bipartisan legislation because the GOP viewed it as 'my way or the highway'. Similarly, republicans simply backed away from any and all debate or attempt to amend the ACA because they refused to work with democrats.

This is the important distinction between what happened with the ACA and with the recent tax bill. Many republicans immediately turned face against what they had previously supported. Which is also a reflection of the modern-day GOP and reflected in how disastrous their attempt at governing has been.