i cannot find Entune App Suite in Apple Store, why?

We are not Apple, only end users like you. We can only speculate and that is deemed inappropriate by the Terms of Use we signed when joining here.

Your best option is to contact the developer and see if they have plans to submit their software for sale in the App store. Some developers do not want to use the App Store, preferring to market their products the traditional way. Other may disagree with strict Apple guidelines for what is offered in the Store