I sit down to play Cyberpunk Red, I know I'm playing in Night City. I read the core book, I know exactly what options are allowed, where my character comes from, even what the slang my character is going to speak, choom. If I play Pathfinder, I'm almost overwhelmingly playing in Golarion and likewise, I know that gnomes bleach, Saranae is the goddess of light, and Absalom is the largest city for miles. I know all this from just one book. And while GMs CAN choose to alter the settings for either C:R or PF, the books are written with the expectation you probably won't and thus exceptions are explicitly spelled out from the norm. If the GM wants to ban rockerboys or set their campaign on Barsoom, it's explicit and obvious the GM is purposefully messing with the intentions of the game.
But good old D&D. You can't tell a player "we're playing D&D" and end that sentence there to fully explain where your game is set. If you invited me to play D&D tomorrow in your game, I could not just grab just the PHB and make a character that will fit in your campaign seamlessly. Well, that won't be utterly generic. And similarly, if I buy Tasha's, I can't even be assured that the material will even fit in your world. If you use an official setting, I either have to buy a second book to read on the setting (though if I'm lucky, on might find a wiki explaining what I need and hope it's accurate). If you are homebrewing, good luck even assuming the options in the PHB are available!
Thus we come to the division that is at the heart of this and many other discussions. D&D isn't a common language: it's a common alphabet and everyone is writing different words out of the same 26ish characters. My hello is your bonjour and despite me knowing every letter in bonjour, I can't understand it without knowing that language first. And people aren't speaking the same language to one another. Well no wonder you get players walking in with an American southern drawl and the DM is speaking Catalan!