I'm not a web developer and I don't know much about programming, but if you have access to this code, then everyone have access it. Or have you found it in a way that is not normally available?
If everyone has access to this code, then anyone can use it too. Well, unless it is protected in some way and what is common for all this gambling platforms is the fact that someone sell them same code, or the main owner give a permission to use it by others..
As you yourself stated, you don't really know much about web development and programming, so don't talk nonsense.

Even if the software was purchased (rented) from someone, it still does not explain the usage of identical verification meta tags. It would be like buying a used car and using the previous owner's driver’s license to drive it (there might be a better analogy, but I cannot think of one at this time). Basically, these specific meta tags are used by Google, Yandex, Microsoft, and other services to authenticate domain ownership, and have absolutely nothing to do with software running on those websites.
Verification is the process of proving that you own the site that you claim to own. We need to confirm ownership because once you are verified for a site, then you have access to its private Google Search data, and can affect how Google Search crawls the site.
Complete information about site verification is available in the
Google Search Console help center.
In addition, I would like to mention that there are other casinos that use 1xBET software and are associated with 1XCorp in some way, but do not use their verification meta tags, which may indicate that they are managed by different companies - which supports my argument even more.