Does anyone other than me think that our Orc characters should be able to become the chieftain of one or even all of the strongholds? Any of my Orc characters could crush the current chieftains. So why can't we challenge them?

You can challenge them, but only to a brawl that makes you a friend of that clan if you win. Given that they are very clannish in nature, it wouldn't really make sense if the player was allowed to take over, since he/she is not a member of said clan., and in fact probably isn't eligible to challenge anyway for just that reason.

I like that one guy chief who seems henpecked, I wasn't expecting that.
But I like the strong no b-s orcish women more!

Never played an orc but it seems you should just rise to thane-like status, if anything. Blood-kin status seems the equivalent.

You could try to role play it, like of your able to kill a chieftain you could role play/"pretend" you became the chieftain. Just visit the stronghold now and then and act like you own the place.

Why WOULD you challenge them? Do you really want to sit around a stronghold, having children and waiting to get old enough for them to kill you? Because, really, that's pretty much all the chieftain does. He certain does NOT go out adventuring, or get involved in the politics of non-orcs.