I am sure free hosting sites could get Adsense before, it was just those with advertisements and popups which weren't allowed.
They are making mony, if you put your ads there too u will get banned from adsense, or just warned .... the speed of light is 300000 km/s so what .... ?
It may be because you don't have control on the content and other ads on the site - therefore you don't own the site so AdSense can't be sure what will show up on the page and probably has received a lot of report issues with free sites violating their TOS
True but they can do nothing about it, the hoster may get informed and close your site directly without even telling you ...