Why 7.5 and 7.5.1 is not called beta?

Probably because “beta” means it is a pre-release version and major changes can be made before the final release. That being said, there is no 7.2, it’s 7.5.20. Also, show me a complex piece of software that doesn’t have “bugs”. I think I can safely say that there are many users that do not have any “show stopping” issues as a result of these “bugs”.