Admit it: for a sole hour of mining, on a most likely general-purpose hardware, which you can use meanwhile for mining, it's not even that bad.

Also consider it's aimed to be mined simultaneously by webpage visitors. If your page can have 10 visitors an hour, that means 10 cent per hour with you doing essentially nothing for it.

For big websites, it potentially means big revenue, especially when combined with, say, Basic Attention Token.