It's a good point, but leads to the reminder that there are many different financial structures for events, and assuming that one is like another can lead you astray.
Some vend themselves, some have a 3rd party vendor, from whom they may or may not get a cut. Some purchase enough merch to cover a full event, and have to deal with the excess if they don't fill. Some have fixed expenses that others don't have---even if they vend and get the margin on the merchandise, if they have to spend $1,000 for the course rental and $200 on PDGA fees and $200 for porta-johns, there might be nothing left for the TD. Some bring in sponsorships, some don't or can't.
The assumption that a TD can make a profit on an event is dependent on a lot of other assumptions---and typically, the idea that every tournament is run the way the poster's local events are run.