Ask HN: Why is there no better protocol support for WiFi captive portals?

I'm curious why we still rely on hacky techniques like requesting captive.apple.com and waiting for interception, rather than having proper protocol-level support built into WPA. Why can't the WPA protocol simply announce that authentication requires a captive portal?

This seems like every public hotspot I connect to it's flakey and will sometimes report it's connected when it still requires captive portal auth. Or even when it does work it's a 15 second delay before the captive screen pops-up. Shouldn't this have been solved properly by now.

Does anyone have insight into the technical or historical reasons this remains so messy? If the wireless protocol could announce to the client thru some standard, that they have to complete auth via HTTP I feel the clients could implement much better experience.