IMO it's the ISP's who are intentionally misleading people. Average Joe might have some inkling of how big a gigabyte is these days, but nobody except a network engineer cares what a gigabit is. I can't imagine how many people buy gigabit fiber expecting a gigabyte. It would sound much less impressive if it were marketed as 125MB/s like it should be. They should at least be required to show both, not make people convert units if they want to find out how fast their advertised internet is supposed to download their 50GB game.

I don't think that counts as intentionally misleading since bits/second is the correct measurement for any serial connection and has been since the days of Baudot. Joe Blow might misunderstand it but that's on Joe.

It's not like the situation with hard drives where they're going against industry convention for marketing purposes.

You could also blame Windows. Linux counts storage bytes in base 10. But still counts RAM in base 2.