I've played in numerous tabletop D&D games. In the vast majority, we don't bother tracking ammo. There have been two where we actually tracked ammo (one of them was even a wilderness survival game, where it kind of makes sense) and it never became close to relevant in either of those games. No one ever came close to running out in either of those games.

I understand that they're physical objects and theoretically, you could run out of them, but how often does it actually happen to people? In those instances, is it because you didn't have the opportunity to get more ammo or was it because you forgot or just couldn't be bothered with it?

I count keeping enough ammo around as part of weapon upkeep. For melee weapons and spellcasters, that they are taking care of their tools is assumed. Why would we put extra work (and tedious work at that, not even fun stuff) on the ranged weapon users?

I could see interesting situations come up if, say, the DM had a little invisible imp running around stealing all of the PCs' ammo - that would force someone who is normally dependent upon their bow to search for less comfortable solutions to their problems. That's something I can engage with. Maintenance, I cannot.