It’s an excellent game, was a lot of peoples first From Software game, and unlike the majority of big titles from that time period, hasn’t been ported, updated or remastered.
Additionally, out of all the “Souls” games, Bloodborne is still the only one that can’t be played at over 30fps.
I think bloodborne holds a lot of reverence because of the themes it portrays. Besides Sekiro, which also has a cult following, all the other Souls games are based in and around medieval fantasy of some sort.
Bloodborne starts in Victorian England with a Van Helsing story and the descends into Lovecraft really fast. For a lot of people, myself included, that’s inherently a more interesting setting than medieval fantasy. People who are into victorian England are really passionate about it, and people who are into Lovecraft are really into Lovecraft.