Because it sounds that much more badass with umlauts.
 

Just an observation, don't really think I need to clarify it. I thought it might be fun to compose a list of artists that contain unnecessary umlauts, either by being complete nonsense or pronounced differently than the umlauts actually imply.

Hüsker Dü
Leftöver Crack
Mötley Crüe
Motörhead
Blue Öyster Cult

I'm gonna need some help. Thanks!

leftover crack has one somewhere maybe over the o