Most dogs bark at anything and everything and often literally nothing at all. We've had so many customers who brought their dogs in and they just bark every few seconds the entire time they're there. And it seems every other time I go to the grocery store there's at least one customer there who brought their dog and it just barks aggressively at everyone that walks by.
In every apartment I've ever lived in I've had at a bare minimum one neighbor with a dog that just barked for hours and hours on end every single day. What could there possible be to bark at for an hour straight at 2am in an apartment? They're just bored. They need constant stimulation otherwise they get bored and bark, and they get overstimulated easily which also causes them to bark. What an annoying animal. I'll never understand why the masses worship such a loud and neurotic animal.