If they already know that why aren't they doing something about it?
Looking at some of these number you can dig further
"The arena's 212 suites pulled in $15 million last season, none of which is included in the league's numbers."
Wirtz owns 1/2 the arena, that brings that number down to $7.5m straight away. On top of that there are non-hockey events, probably many more than hockey events. Bulls play there, that reduces the hockey revenue part from 100% of $7.5m to way less that 50%, probably closer to 33% at best. That $15m is now down to $2.5m. Add in running costs for the rink etc and its getting smaller and smaller not mention Wirtz is entitled to some profit as 1/2 owner.
There is a heck of lot more going on at the United Centre than Hawks games (
http://www.unitedcenter.com/). Why should it all count as Hawks revenue.