I fully support playing through the backlog before buying new games, but you also shouldn't force yourself. When I finish a game, I go through the list of all the games I have (don't have much bought games in my backlog, but with PS+ and NSO classic games, have quite a big library of games that I can play without paying), and see which one I feel like playing, and then start that.
Of course, sometimes you want to play a specific game, and just get it, but in general, I try to keep my buying games at minimal.