This is a load of crap, and you have no idea what you're talking about. Let's do some simple math, take a 10,000 person convention:
Assume 150 vendor booths at $1,000/booth = $150,000.
10,000 people @ $50/person = $500,000 (note: Anime Central 3-day badges are currently starting at $63 going up to $80 if right before the con and they reported attendance this year at over 30,000 people, Meaning, at MINIMUM, attendees represented around $2 million in revenue (assuming EVERYONE bought the cheapest tickets possible), The MOST expensive vendor booths currently cost $1,400/booth, so they'd need to sell almost 1,500 of them to match that number, they did not)
And I can also guarantee that 90% of cons are not getting any (monetary) kind of "sponsorship". There's well over 100 cons across just the US and the major anime companies attend maybe 10-20 of them. CrunchyRoll decided to cut out the middle man and just runs their own con now. The vast majority of cons are not pulling the majority of their revenue from vendors & sponsors. Anime Expo probably has the best "sponsor" situation and they pull nearly over 100,000 people at almost $100/person (not counting "premium" passes which are closer to $500), that's EIGHT figures from attendees.
