Some broadcasters view/use Freeview as a marketing tool and will broadcast a channel FTA on Freeview in the hope you'll seek out their other subscription channels on paytv platforms.
Some channels are only present on Freeview in the first place because the satellite subscription money they receive in part funds them....
The channels that are available on Freeview but FTV (Free To View - free but encrypted, so require a Sky viewing card/box) on satellite are encrypted for two reasons, they've done an 'exclusivity' deal with Sky i.e 4HD. Or because of rights issue's,