It makes the most sense for a real push, and would also help explain why the movements in Zap/Donetsk have been so cautious. There's lots of unwinding of established Russian hard points to do there, so a certain lack of pace is expected, but they also haven't pushed advantage aggressively at all when it's been there if it would put their forces in any sort of position to be countered.
I really think they've been waiting for the Russian fuck up in blowing the dam to mature (the river banks drying up enough to create additional easy landing areas). Never interrupt your adversary when they're in the middle of fucking up and all of that. It's the longest supply route with the easiest terrain to advance in, it creates the options to turn the Zap defensive line into a 2 fronted war, and if the Kerch bridge can't be used, basically turns Crimea into an island.
It's where Russian forces, logistics, and current political philosophy all meet at a weak point. Re taking Bakhmut would make a statement, but forcing the surrender of Russian forces on Crimea would likely be a regime ending moment, without having the take back every metre of territory in the east the hard way.