There's no reason why having the back catalogue in streaming should be different from having it in DVD .. except that streaming has opaque accounting and seemingly pays terrible residuals.
Licenses are written before the technology is invented. Originally we had radios and record players. Each new medium requires a new license due to the structure of the ownership of the content.
Publishers that own images for print can't post them on the web. The problem is the exceptional nature of the contracts. This is why things are so splintered. All the acquisitions of corporations may create even more exceptions to the licenses.
If you have an original DVD collection of The Boondocks [1] then you have the episode
Boondocks, The S03E04 The Story of Jimmy Rebel
banned after first showing on Adult Swim for excessive depictions of racism and perceived racial insensitivities over the episode's portrayal of a racist country singer named Jimmy Rebel (a parody of real-life white supremacist country singer Johnny Rebel). [2]
There are many other examples of broadcast episodes still available on DVD, BluRay, torrents, and still indexed on IMDB theTVDB etc. but not available via online streaming.
The difference is that DVD collections were mostly created by movie fans. You had a small, but loyal audience of people that would wait every Tuesday for releases similar to movie releases.
Getting $20-30 per DVD from this audience was much more lucrative than the cents you get per stream when competing against the algorithm of "what should I watch next". It's a VERY different market now. Smaller stuff just doesn't compete.
Once you remove the need to personally curate and review (think also towards the death of the film critic), you introduce a homogenization to the industry.
Streaming is fantastic for convenience. It is terrible for variety, despite the illusion that we're overloaded with choice. The modern streaming system hides everything in plain site. It is almost impossible for me to "browse" streaming sites the way I used to in a Blockbuster or Best Buy. Discovery is much harder.
