Interesting perspectives. For whatever little it's worth, for me it was just last summer that I got it into my head that I was finally going to do this thing I'd kind of idly fantasized about for a while, and at the time the only certification I'd heard of was PADI. I think my initial internet search might even have been for something like "PADI certification Los Angeles" as opposed to "learn to scuba dive." The first I heard of any other agency was in my OW course; one of my instructors was originally NAUI certified. They have become, for many people around here who know little about diving, pretty much synonymous with the sport.
I've had some mixed feelings about the OW course I took; I kind of wish it had been more thorough, but I also recognize I wasn't as committed to the idea then. If I'd had a choice between the 2-weekend PADI course and, say, an intensive monthlong program, I probably would've picked PADI. If the monthlong program had been my only option, I might not have bothered at all. Now, though, I've taken multiple courses and I want more; I'm hoping to do LA County's intensive 2-month advanced diver program next summer. PADI made diving seem fun, low-key, and approachable, and it can be, if you're just following a DM around a tropical reef. But it wasn't long before I wanted more than that. So I can see the value in the low entry bar, and I don't really regret starting where I did. But there's so much more out there that other agencies seem like they might be better for, and I'm grateful to this board for educating me about them.