Why doesn't roku offer live streaming of abc, cbs, cnn, fox, nbc and other channels that are free with a tv antenna. to obtaining these channels requires joing other paid subscriptions and more than one that should normally be free to watch.
All has to do with rebroadcast fees.
Occassionally, a new channel will try to provide streaming access to local channels for free/minimal charge, but then have legal action brought against them by the broadcast companies. Rebroadcast fees are reportedly a billion dollar business/revenue strategy for them and they are not about to let other services provide access to local programming for free.
Locast was the latest streaming channel to meet the above fate.
(https://www.digitaltrends.com/home-theater/lolcast-shuts-down-how-to-watch-ota/)
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As a streamer, only real way way to get local/OTA channels is still via an antenna connected to your TV or a tuner device/DVR, or to subscribe to a streaming service that offers live local programming (which reflects this service in the higher prices).