They must see it as some sort of reverse tit-for-tat. Now both sides have "nuked" a dysfunctional part of Senate procedure, so any future "nuking" is less likely. Certainly by the GOP. This was inevitable, might as well get it out of the way, and they can use the "bullies in the GOP are responsible for this" narrative starting today.
The dems are thinking they get to be the first to nuke legislation next time they own house, senate, and presidency.
They see single payer in their future.