[...]
Like you rightly said, building a software from scratch involves a lot of work, which might take years due to how much time that is needed to test and correct every error before releasing the software to the public for use, hurrying to release a half baked software can be very detrimental to the business, as hackers can easily identify an error and use it to hack the platform.
I would even go a step further and say that writing the software from scratch will most likely result in the casino not surviving for long:
In addition to the very high costs (development team, testers, ...) for development and, above all, maintenance, it must be assumed that the software will not function smoothly, at least at the beginning. On the one hand, this naturally concerns bugs that annoy customers, but it can also lead to customers exploiting errors in the software and the casino losing a lot of money. There have been more than enough examples in the recent past where casinos have lost thousands of dollars due to such bugs.
If you use standard software, as whale.io does, this risk is significantly reduced. Even if errors do occur, it is quite possible that it has been contractually agreed that the casino is not solely responsible for rectifying or compensating for the damage.
The use of standard software is therefore highly recommended, especially for new casinos on the market. You can always replace parts of the software with your own developments at a later date ... if you really want to.