Captive portal detection is endlessly buggy.

That's explicitly why captive portal detection does not use HTTPS. If your OS of choice fails to detect captive portal (or doesn't implement detection), and you have the ability to visit a website, you can visit example.com to get into the captive portal.

The really annoying part is when a device (cough, Switch at launch) doesn't have portal detection nor a web browser, making it useless on hotel wifi.

I guess one could bring a laptop, spoof the Switch's WiFi MAC on the laptop and use it to login through that portal, and then disconnecting, and connect the "authorized" Switch. And make sure the Switch doesn't have "randomize MAC" like on Android/iOS.

But that's a huge workaround for many.

Yep I've done it. What a pain. Thankfully now the Switch does have captive portal detect and a little purpose built web view for agreeing to the terms.

I could see some forms of advertising or spam (or scams) preferring this.