By passing the casinos ip block using VPN
I Wonder why someone would want to go through all that stress just to risk his money.
Bonus abuse is one reason. Especially if the casino provides no deposit bonuses and similar benefits. Abusers will try to sign up using multiple accounts, hoping not to get caught. Another type of abuse is that from returning players who were banned in the past and they want back in.
I've only seen a few casinos that restricted me by IP of my country, but I hardly witnessed that. Among over 200 casino sites I'd visited, maybe just 3 of them acted that way.
You are from Nigeria, no? Most casinos on this forum have Curacao gambling licenses. This licensing house doesn't restrict Nigerian players by default. If you were based in Germany, the US, the UK, the Netherlands, etc., you would probably notice it more often.