There are better systems, for example RFC 7710 defines how DHCP and RA (the methods devices use to get themselves an address from a network) can tell a device about a captive portal, which is the thing that hijacks your access to the Internet and tries to show some sort of "login screen". There's a current IETF working group, capport, doing 7710bis and other work in this area.

But the existence of a better solution doesn't stop people doing something crummy that kinda-works for them. That's what you're seeing today, it's what you see in most places, most of the time. That's people.