I think it's because of the competition between casinos with the same business as other casinos. It's normal to see other sites hire other people to attack other businesses so that the attacker's site can benefit from the site's inactivity.
I didn't think much of it because I'm sure the casino sites would be able to handle it well. The security team from blackjack.fun has experience dealing with attacks from competitors. And we have seen blackjack.fun being active again now.
We never know where is this coming from, could be from a gambler who loses too much money or just to test their skill in how they do DDOS the most important thing when you are a site operator or a webmaster is to Implement server-level DDoS protection and Remind yourself that you can be DDOSed even if you are a big or small site, I'm sure Blackjack.fun server is good enough to combat DDOS in the future, glad that they've fixed it quick.