Prior to D&D, to my mind, there was a high, hard wall between D&D and all other RPGs. Or, I suppose more technically, between TSR and all other RPGs.
(Note: I did not live in the midwest)
It felt shitty when I was in a hobby which was "D&D and also those other games" and I really like it when I am in a hobby of "RPGs, like D&D and also.." and I am fearful of swinging back to the old ways.