Each casino must define to whom its offer is directed and how it can be used. For many players this is already decisive. Imagine you come from South Africa and are looking for an online casino. Not every casino accepts players from there. Then you should only consider those casinos that accept you as a player. Otherwise, the best bonus conditions are of no use to you.
The same applies to the currencies offered which can be very different from casino to casino. There are casinos that accept a very large number of currencies, others again only accept a few such as USD and EUR. I would say that if you come from an EU country with euros you will find 95% of the casinos today that also accept euros. USD accepts basically every casino, unless it is a pure Bitcoin casino. And then we are already at the complex topic of crypto currencies. Because anyone who wants to play with them must expect that almost all of the major brands are no longer an option. Unfortunately, Bitcoin and Co have not yet established themselves so well that they would be a topic for the big players. They prefer to leave this segment to smaller casinos which usually offer a wide range of crypto currencies.