Well that's a first, I mean all my registration on various casino, I hardly see Nigeria restricted and it would really interest me to know why some many countries restrictions on your platform.
The reason could be that they are either still going under those countries regulatory requirements and registration or they don't want to get licences from them, and as such, allowing people from those jurisdictions to play in that casino is going to make things a bit complicated for them as regulators from those regions can come for them for illegal operations.
But I see Nigeria and some other African countries having a gambling-friendly regulation that any casino can easily reach an agreement with and allow their citizens to be part of their customers. It's just a matter for the casino to decide if they want that or not, and they can get the licencing done.