I think Misfits cover bands are so many in number is because the songs are easy to play and who the fuck (besides big gay D-Man) doesn't love them. The sing-along levels of the songs are unmatchable. We started off doing just Misfits covers but eventually worked some other stuff in there like Cash songs. Good times.
If you know how to play two Mistfits songs, you pretty much have the potential to play them all, at least on guitar. The lyrics are also ridiculously easy to learn. I mean, let's look at some of their lyrical masterpieces....
20 Eyes said:
20 Eyes in my head
20 Eyes in my head
20 Eyes in my head
They're all the same
They're all the same
or this little ditty's classic chorus...
Where Eagles Dare said:
I ain't no goddamn son of a bitch
You better think about it baby
I ain't no goddamn son of a bitch
You better think about it baby, babe.
or my personal favorite...
Die My Darling said:
Die die die my darling
Don't utter a single word
Die die die my darling
Shut your pretty eyes
I'll be seeing you again
I'll be seeing you...
In hell.
The number one reason there are lots of Misfits cover bands though? Because like Armbar said, they fucking rock. It's fact, even if you don't like them, they rock. A guy smashing the drums with a cymbal shot thrown in from time to time, power chords, and a screeching lead singer... that's all you need, and that's rock and roll in it's most simple form. If you can't appreciate that, then you're at the wrong show anyway, grandma.
Edit: I was never in a Misfits cover band. But, and I'm not joking, I was asked to be in one, and we jammed one time before the lead singer decided he didn't want to do the Misfits cover band idea anymore. He went with a ska band later.