Or is it more that you've grown accustomed to them over time?
I'm more a Nintendo gamer, but I've always had a Sony console as a secondary option, usually one generation behind. So it's not like I can't use a DualShock or have trouble with Square/X/Triangle/Circle.
It's more that I don't see the point of using those symbols. You rest your hand over the PS controller in the same way as the others: thumb hovering over the leftmost buttons so you can hold the top one while pressing the bottom one. The right buttons are usually secondary inputs since you'd have to move your thumb from the default position. So in that way, the PS controller has the same general "feel" as the others.
It's fine once you get the base controls down, but what about fighting games, sports sims, or other games with more dynamic inputs? On a Nintendo or MS controller, all I have to do is memorize the input and I'm good. With a DualShock, I have to memorize the input AND translate the symbol to a particular button. In theory, you'd have to do the same with A/B/X/Y, but at least for me and others I know, that process is automatic with letters/numbers, but noticeably slower with abstract symbols.
Is there some benefit to using symbols that I'm missing? My research indicates that the symbols originally had more distinct meanings (eg square for menus), but it's clear that this was never enforced or used consistently. So I'm stumped on this one.