Why don't they allow external servers on consoles?

Hello, I find it frustrating that a user, in this case myself and others, buys PS Plus for PS5 or any other subscription to play online, only to find out that you can't add external servers and the ONLY thing they offer are the same seven sad 'featured' servers, as if we had more options to play. At this point, I think I'd ask for a refund for the game on my PS5. Why is it so difficult for them to add the 'add external servers' button? I don't see the problem with it. In fact, I consider it a real investment, because when people see that they can add external servers, they'll buy more to play. Thank you.