So in "A Blade in the Dark" you find out the dragons aren't just coming out of nowhere, Alduin is specifically reviving them. Nowhere does it state that dragons other than Alduin has the power to revive dragons. So why is that when you not only kill Alduin, but go into the afterlife and re-kill him, are the dragons still randomly spawning? It makes sense gameplay-wise as you want souls for your shouts (and see the higher level dragons too later on), but story-wise it doesn't make sense to me.

Not only do the dragons randomly spawn, but the dragons at fixed locations also REspawn, like they've been re-revived.

He's been very busy...

In all seriousness, notice the large amount of dragons leaving the Throat of the World when you talk to Odhaviing (and Parthunaax if you didn't kill him) at the end. In the time you spend dungeon delving, traveling, and questing, Alduin could very well have revived countless dragons. He is the son of the time-god after all.

I guess that's just as plausible as the exact same number of random bandits setting up camp in a dungeon you've explored after only a month.

I guess those 1000+ dragons all hide behind clouds until they see a defenseless mudcrab, then attack.