This isn't generally a problem on smartphones and tablets because they can usually detect captive portals and prompt the user appropriately.
I don't travel often (Christmas and maybe once or twice a year outside of that), but it's when I encounter this. It's very frustrating because I'll be walking, pass a store I've previously connected to Wifi, and suddenly lose Internet, then hunt for a website to get the portal to pop up.
I'm annoyed that captive portals have been commonly using DNS hacking since 802.11b and I'm surprised a better solution hasn't been standardized. I have no idea where in the stack it should go (DHCP, wireless standards, or whatever) but DNS hacking drives me nuts.
The experience has gotten a lot better. I see Apple's pop up covering a lot more corner cases, but after years I see have problems almost every time I travel.
The most sensible option would be a DHCP extension that indicates you are behind a portal and gives the IP to load, but this requires updates to every DHCP server and client, so it would take many years before it works reliably. Also, it fails for IPv6, but a modification to the Router Advertisement message could maybe do the same thing. It's a little scarier in this regard because it would be even easier to abuse.