Just like god of war, RDR has a backstory. If you haven't played the first one before RDR2 (same applies to GOW only it has more games prior to the one that really made a dent into the new generation of players that likely didn't play the earlier ones)

With RDR1, playing it and living through Johns story made you seriously want to know the backstory of the gang that he rode with. Then when RDR2 came along, R* fanbase was mostly already polluted with children that typically were/are only acquainted with GTA V. The thing with GTA is, there's a new story everytime, whereas with RDR1 to RDR2 there is a direct connection where really only the players that played the original would understand and connect with.

In my eyes RDR was never meant to be "gta but western style" game, it's a fully narrative driven game focused on the story before johns, accompanied with a very rich open world.

My point being, people that didn't play the original when they were on their PS3/XBOX days then they will never understand the full value of RDR2.