stalebrim Why can't solus budgie alleviate its problems by making Nemo the default
I don't know why Solus sticks with Nautilus.
Nemo is a fork of Nautilus. Nemo forked about a decade ago to keep features of Nautilus 3.4 that were removed from Nautilus in 3.6 and following. Of course, Nemo has been on its own development path since the fork. Nemo has developed into a well-regarded file manager.
Ubuntu Budgie made the decision to cut over from Nautilus to Nemo in 2019 as a result of UB community preference for Nemo. Nemo/Nautilus preference was discussed repeatedly 2017-2019, and sentiment clearly favored Nemo, as Nautilus diminished in comparison.