There are a number of reasons why (some of which I'll cover later), but at the core is this: they have plenty of individually powerful cards, along with powerful tribal bonuses
If you have lots of protection, things like countermagic, Spellskite, Lightning Greaves etc then these cards improve in value
The ward 1 doesnt matter so much in Commander, but it can still pull a gotcha
If Delina is your red commander, its easier to build around it since having this copy ability in the command zone is very strong
This one can be wonderful for sneaking encoded creatures through, but with Dimir and Orzhov players out there there will be black creatures all over the place
Madness doesn't give you another chance to cast it later