I have noticed a trend that some of my friends accounts get rate limited extremely easily while others don't. Not sure what's happening there, I assume there's

I have noticed a trend that some of my friends accounts get rate limited extremely easily while others don't. Not sure what's happening there, I assume there's a flag set by a mod or its otherwise calculated by karma total number of times the account has been flagged. it doesn't seem to correlate with recent controversial posting