How is this allowed?

So I paid for the full game, which was 5€ or so, then they added 30sec adds in an update. Now theyve changed it to a free app with with in app purchasing and more adds. I dunno how this is even legal... Dont dowload this app and support this kind of behaviour. The game is also not good.

Dr. Nooble about Heroes Reborn: Enigma, v2.1.0