Because a lot of what's in CK2 never gets used. When's the last time anybody used their chancellor for anything other than fabricating a claim?
I frequently use my chancellor to improve relations. When you play pagans, which I generally do, there's less need to fabricate claims.
Or the steward for anything other than collecting taxes?
Again, when you play pagans, you end up spending a lot of time as tribal, and using your steward to settle your tribe. And even when feudal, I sometimes use my steward to speed construction, and even to research tech. Once you're feudal and have a fairly large realm, the extra money that your steward might occasionally manage to collect isn't usually that significant.
Or the college of cardinals?
Got me on that one. Even when I play Catholic, I've never bothered to worry much about the College of Cardinals.
I bet less than 0.1% of players ever play in India, or as a nomad, or as a republic...
I've enjoyed playing in India. In fact, my current game is as the Emperor of Tibet (which isn't exactly India, but wouldn't make much sense without India). OTOH, I've never seriously tried to play as a nomad or as a MR, though from reading the forums, some players seem to prefer playing as nomads or MRs.
and I don't think anybody enjoys the Muslim decadence mechanic.
I doubt anyone enjoys it, but it's there for a reason. Unfortunately, the mechanic doesn't quite work right. Still, that means it needs to be fixed, not thrown out.
How many people ever play a start date other than 769, 867 or 1066/1081?
I have to admit that since I bought Charlemagne, I've never started at any date other than 769. I haven't even tried the new Iron Century bookmark. I think some people like the 1337 bookmark.
How many people play as a tribal and enjoy it, rather than rush to feudal?
I think that tribal gameplay is actually more fun than feudal gameplay, but at least pre-Holy Fury, it made sense to feudalize fairly quickly, because as technology levels went up, tribals became increasingly outclasses (which is historically accurate and appropriate). The changes made in Holy Fury make it at least somewhat reasonable to stay tribal for the whole game.
How many people ever use a succession law besides ag-cog primo or ag-cog ultimo?
I don't know the number, but some people actually prefer other gender and succession laws. Personally, I want primo, but generally favor agnatic over agnatic-cognatic.