It takes way too long for enemies and dungeons to respawn. even plants take 10 days in the open world, and that is if you do not enter the cell. Can't Bethesda fix that?

That depends if you are on pc. There is a mod out there http://skyrim.nexusmods.com/downloads/file.php?id=6176 can fix that up for you. In the last game Oblivion it had a three day timer. The game before that one Morrowind did not have one. After you clear that area out it stay cleared. If you on console? Bad luck.

While you wait, go explore the other 300 dungeons in the game.

*google*

skyrim respawn mod

you can set the number of days for respawning

i have it set at one day, so there are always things to kill

some dungeons dont respawn though. no idea why...

No Bethesda, don't fix that - it's perfectly fine as it is.

there are hundreds of dungeons. the spawn rate is fine