marvelmole-
Good catch by Strega -- I missed it.
Cable-type channels want to be paid. When you have a paid subscription to a "tv provider" service that carries these channels, the channels receive their pay out of the subscription fees you pay that provider. When you don't have a subscription to such a provider you are not paying for those channels.
Many cable-type channels (including Hallmark TV and History) make their content available for streaming on the internet via a "TV Everywhere" channel app for those paying for the channel through a provider as mentioned above.
Are you subscribed to a paid service that carries these two channels? If not, you can subscribe to one of several premium subscription services that runs on Roku and carries your cable-type channels of interest.
There are several places on the net where you can look up which streaming providers carry a particular channel of interest. Here are several such pages:
• https://thestreamable.com/channels
• https://www.groundedreason.com/cord-cutting/tv-streaming/how-to-stream-by-channel/
• https://suppose.tv/ (thanks to @DBDukes for this one)
• .. there may be others.
Savings in cord cutting usually come from picking and choosing which of the offerings you wish to pay for instead of paying for full blown cable or satellite services with scores of channels you never watch.