I have tried to market bubble parties around here but so far there has been little interest.
young...

My market already has the established "Bubble Guy"... in fact, Bubble Parties were invented here. However, that reason aside, it's simply not an avenue that I choose to focus on.
What about the cost of liability insurance?
You mean by John Allo? With absolutely no disrespect to John, as I was friends with him, who knows who really "invented" them? Certainly he was the first person I heard of doing them, but it would not surprise me if some non DJ forum DJ hasn't been doing it for a ton of years...
Other...I just don't see that there's enough of a market around here to make it profitable.
Ok, that's gonna be nearly close the total number of daycare centers in our city.