Yea ik but something doesn't have to stop getting bugfixed/improved after it's out of beta
The thing is that PS is an on going project that is constantly changing and evolving. Also as new pokemon come out and new generation mechanics are introduced its so much easier to remain in beta and execute these additions/changes than to release PS then require these changes to be installed.
One of the major selling points for PS in the beginning was that it wasn't like PO you didn't have to download patches and updates. It was all in the browser.