Edit: it looks like that rate limit was put on your account several years ago. I didn't look up what was going on at the time, but I've taken it off now.

(In the future, I think we'll probably make penalties like this expire after a while - the problem is it's not so easy to tell which accounts are still breaking the site guidelines vs. which ones are fine, short of manual review, and we don't have much capacity for more manual review. In the meantime, anyone is welcome to ask what's going on with their account and we'll always take a look and answer; and when it seems safe to remove a penalty like this, we always do.)