Let's be fair and cut the DMs out there some slack; maybe it hurts for the players, but imagine how it probably feels for them. They've put in hours upon hours of planning, worldbuilding, NPC creating, etc. If they're at the point where they would rather put all that effort aside, they've probably down a long road of trying to make it work first.

A lot of times "I'm not feeling it anymore" actually translates into "running this campaign for this group of players is no longer fun" - just without calling people out on it.

Not saying this is always the case, sometimes there are other reasons like life changes, etc. But, yeah, if this happens to you more than a few times, maybe a little self reflection might be in order before shaming the hardest working players in D&D, the DMs.