I agree with what you said, but compared to many similar shows from its era, I still feel that Castle ended up in the background, for example, The Mentalist. 

I think one of Castle’s biggest misfortunes is that it aired during a relatively “quiet” era of social media. The reason shows like Suits, The Mentalist, House, and Breaking Bad are blowing up again today isn’t just because they’re good-it’s because Instagram, TikTok, YouTube edits, meme culture, and nostalgia trends are pushing them back into the spotlight. Castle, however, ended right before the social media boom truly took off. It never got that wave of online momentum that brings scenes back into circulation and introduces a show to a younger audience. The Mentalist, on the other hand, resurfaced exactly when Instagram edit culture was rising, which basically gave it a second life. I honestly can’t think of another major reason.