why do some poker opponents never bluff ever

i've seen a ton of folks at low and mid stakes who literally never pull the trigger on a bluff. like not even a small semi-bluff, just pure value betting every hand. it's weird because sometimes the board is screaming for a bluff but they check it back or insta-muck to any sign of resistance. makes me wonder if they're just way too risk-averse, or maybe their experience is mostly against calling stations so they never got “punished” for playing that straight.

sometimes it makes reading their range super easy. just value hands, almost always. but i keep wondering if i’m missing something about why people would stick to this, even though a basic mixed strategy seems better.