The Top Ten reasons why the ASOE still use Mumm-Ra as their puppet when he continues to fail. 

Special Mentions: 

All of his excuses are at least good for a laugh, and they enjoy making fun of him behind his back (Cheeezey) 

Because Rameses asks too much for a salary. (Pedneau) 

Because to use Luna....well, they might as well do it themselves!(Brainape) 

They're recruiting him to be an exotic dancer for their new club called "The Evil Ancient Spirits Café"(MetMutt42) 

Mumm-Ra is the only person ASOE could fine to do evil work for free (MC68040) 

Because he works for penis... er... uh...peanuts. Yes that's it peanuts. (OpiePowers) 

His mummy wrappings make for good strings. (OpiePowers) 

The Ancient Spirits of Evil like the feeling of their hand up Mumm-ra's ass. (OpiePowers) 

Two words: sexual favors (OpiePowers) 

Because Mumrana was getting her nails done when the ASOE were recruting 
(Catonis) 

They like to pull his strings (Barlemon) 

They think Mumm-ra looks really hot in his mini skirt/robe and stylin bandages (Mat0014) 

Because he's so damn cool. I mean, who else (besides, say, James Earl Jones) 

could get off repeating that chant every episode he's in?(Nick Gardiner) 

Because they like shoving their hands up his butt. (Lindsey M. Doering) 

ASOE: "What can we say? The man works cheap, and 'Snarf-Ra the EverLiving' still makes us wonder what in Jagga's name we were smoking!" (The Snarf) 

Satan was busy (The Snarf) 

They lost the bet (The Snarf) 

His contract allows infinite failures. (LeoLion) 

Here is da Top Ten! 

10. He has a LIFE time contract (Drakon2220) 
9. Their wives made them (The Snarf) 
8. He will do whatever you tell him if just give him a cookie. (OpiePowers) 
7. The ASOE can't get enough of Mummra calling out their name!!! (LionO5682) 
6. Ma-mut can't do it alone (OpiePowers) 
5.  The ancient spirits of evil wanted Horny-Ra, but he was already taken by the ancient spirits of XXX.(Gatotrueno) 
4. They get off listening to him grovel and beg for their forgiveness (Cheeezey) 
3. If mumra were to win the asoe wouldn't see Lion-o's sword grow anymore! (Barlemon) 
2. Can anyone picture Luna as Bitch-Ra The Ever Bitchy? (Mat0014) 
1."Mumm-Ra, the Ever-Living" sounds cooler than the only other being evil enough to fit into their plan: "Barney, the Ever-Purple" (Joe)