Casinos often start with available games from trusted game providers because it provides them faster way to build up their platform with enough good games for users. It helps them to have users who love most common games from those game providers too. Developing own-built games is not easy and there is chance of success or failure so new casinos must consider this risk factor carefully before spending their budget for own-built game developments.
They will never use all available budget for this development task but in long term, if they succeed with own games, they will have very good chance to get loyal users who love those games that can not be found on other competitive casinos.
It is normal if casino have games from trusted game because they want to attract attention from gamblers. They just need to prepare their casino so that can run without a problem. By having so many gambling games available on their casino, gamblers will like to playing gambling and spend their time. They will satisfy to choose many gambling games and hope they can win the money.
The casino owner know how to allocate their money to every department so they can run their plan one by one. Besides that, the owner will have reserve funds just in case if there is an urgent situation so they can use that money immediately.