[mythtv-users] slightly OT: cable/dish vs ota question

[Evuraan]

i recently ditched my cable provider and switched to OTA using a
hdhomerun (us).

i like the OTA lineup and functionality mythtv extracts out of it -
which makes me want to ask this question:

how do big TV networks "treat" OTA transmission? I understand
subscription based channels sticking to cable/dish tv distribution
with their encrypted stuff and all - but why aren't others switching
to (or atleast, adding) ota transmission which will enable them reach
more regular viewers. Or are a few of big TV networks contemplating
this now that the DTV switch is complete in US? aren't they loosing ad
revenue by staying just on cable/dish networks and by failing to reach
ota viewers?

any helpful pointers will be much appreciated.