It's sad that someone would hack a site like this. The only thing they could possibly want are the email and password combinations. I hope they are stored in a secure way.
1) a novice hacker looking for experience 2) an automated bot that scanned IPs for some vulnerability and acted on its own when it found one 3) someone looking to extort the owner for money 4) someone with a personal vendetta against the owner 5) someone looking to secretly plant bitcoin mining software on the servers (who got caught) 6) someone looking to alter their own score to help them get some sort of math job
I could probably go on for a while, but you get the point. It's hard to ascribe intent to this sort of thing without more information.
I like #2 though, or as I'd put it: flotsam of the internet, like how slammer ended up at davis besse.
According to this https://news.ycombinator.com/item?id=8181773 then don't even store emails anymore.