Yes there is competition for streaming but not for the specific content of the services. With music I can choose Spotify or Deezer or whatever, but for Disney content I can only use Disney+ or for Paramount Content only Paramount+, so they have a monopoly for their respective content if I want to stream it.
That's most industries though. That's like saying Toyota has a monopoly on Toyotas but, I can just buy a Ford that does the same exact thing. That's not what monopoly means.
That's not a very good analogy, but even if we run with a cars one... then it's more like one dealership being the only one allowed to sell Toyotas. You aren't allowed to buy any Toyota, even a used rusty one, from any other dealership. If the dealership decides it costs too much in storage to keep a certain car, like a Prius c, in stock...well they just get rid of the Prius C altogether. (HBO and Westworld being the dealership and Prius c for example)
Not really. That's a different media and format. (But before you say that you can technically stream it on DirectTV too, that's owned by AT&T, who also owns HBO)
But sure, I'll accept that Westworld wasn't a great example for my analogy since I was only considering streaming. A better example might be Final Space Season 3. The third season never got a physical media release (any you find are homemade copies) and the entire series is unstreamable (save for s2e1 on Amazon prime for purchase....for some reason).
This is going to be a growing trend. If they ever decide to pull streaming rights for Barry s2-4 or Stranger Things S3-4, they also don't have physical media available currently.
I agree that what you're saying is a problem but, that still doesn't qualify it as a monopoly. If one company owned every TV series that's a monopoly, what you're saying isn't.