That's because Sweden joined the internet relatively early when enough addresses were available. It's like that in most 1st-world countries. Places like Argentina, on the other hand, may have to share 8 IPv4 addresses per city.

Wow a publicly routable IPv4 address on a mobile phone? Wouldn't that drain the battery a lot? Or is there some kind of carrier-level firewall still?

Telia does it for mobile, I think Tele2 and 3 as well? Bahnhof, Bredband2 and other small ones also use it for wired customers, but you can usually get a public if you ask for it.