Most of it seems to be first-party streams of content which is also available as unencrypted over-the-air broadcasts.

It is paid for via ads or subsidies, so there's no reason to block access to the stream, so they just don't bother, and make life easier for anyone building streaming devices wanting to integrate their channel.

Someone accessing the stream directly is not the originally intended use case, but it isn't any different from someone accessing it via their smart tv.