It's the light caps... regardless of how much time you invest you don't get stronger...most of the numbers are functionality useless they only exist to make you think you're making progress but you're not...it's a practiced psychological hook...
Light cap use to mean something, but ever since Final Shape, Bungie took that away thanks to power disabled/minus power. It was one of the worst additions to the game they have made. Part of the reason is because of tryhards out there saying the game is too easy, mainly complaining about raids/dungeons, but they were playing the base version of those pieces of content. They completely ignore Master difficulty for them, but still complained and now things like base raids/dungeons have you at -5 power of the recommended at all times. GMs put you all the way to -25.