Hello - yes April 21st is the same weekend as the Ohio Academic Competition regionals competition. That is one of the things that will keep teams from attending. Here is a link to the Ohio message board: http://www.createphpbb.com/oac/
where you're more likely to come across prospective teams that may attend, and there you can talk to coaches and members of the community that can give you more helpful insight and information than a student like me can.
If you want a bigger turnout for your tournament for future reference, you should buy from a reputable vendor; such as High School Academic Pyramid Questions (HSAPQ) or National Academic Quiz Tournaments (NAQT). I see that you are the advisor from New Albany H.S., I believe we played your squad at the Ohio State winter tournament in January. That tournament used questions from HSAPQ, and they are generally considered to be an excellent series in part to its length, distribution and difficulty. Both companies write their questions in the tossup/bonus format, so what you guys played at Ohio State in January and March resonate the popular format in Ohio. If your question source changes to HSAPQ or NAQT, you'll likely to see not only a higher number of teams in attendance, but teams from a wider area. This is because Ohio is full of teams that play lots of tournaments and build from their performances (i.e. Olmsted Falls, Warren G. Harding). To quote the great movie Field of Dreams
"If you build it, they will come". HSAPQ and NAQT questions are the preferred sources of academic pyramidal quiz bowl questions in Ohio.
The school I'm from; Fisher Catholic, is from the metropolitan Columbus area as well (Lancaster). I can't speak for my coaches, but if this was a.) on a date that worked well for is and b.) had questions from a reputable vendor, we would probably attend since New Albany is not a far drive.
It's nice to see another Franklin County school getting in the saddle. Hope to see you guys at more tournaments, your squad looked good both times we played them (the second time around in March, we were the team that wore the beards).