One with everything will be far more expensive than millions with one thing, and if you disagree with the service you wouldn't be able to switch to another one.
One monopoly on streaming means they'd probably jack the prices up a lot since they would be the only legal way to watch things (and theyd probably crack down on piracy even more)
Multiple streaming services at least helps keep prices at a reasonable level
Hard agree though that exclusives are the worst thing streaming services adopted