I used to have one in Foot Stomp long, long, ago. While the chances to proc are low on AoEs, each target has a chance to set it off. If you are footstomping in a crowd, you get the proc to go off most of the time.
If you have a 1 in 5 chance to go off, but 10 targets, what are the odds that it will go off at least once. Don't ask me. I dropped Statistics in college and that was decades ago!