Quality of the game has little to do with it's popularity, people seem to buy obviously mediocre games just because they feel like buying them (because of a recognizable title, familiar characters, high fidelity graphics, memes, streamers, open worlds, casual word of mouth etc). People that say the game is not good enough or too hard or whatever completely miss the point. In order to know whether the game is good you have to play it first which not many people did obviously, at least compared to popular slop.
Objectively NG4's "problems" were lack of proper marketing (I learned about it through 4chan, not the helicopter stunt) and recognizable characters, as well as uninviting visuals (it doesn't look too fun on 480p video) and honestly just the fact that this autumn was fucking stacked.