They don't carry old TV miniseries. They don't carry many older classic shows. They don't carry many old classic movies and especially not more obscure ones. They don't carry many artistic/indie movies. They don't carry many foreign movies. Sometimes when they do carry something it's edited all weirdly, unlike the original (perhaps because they didn't get the rights to use the music or other stuff in streaming).
I still like the streaming services for what they do carry and especially for the serendipity of browsing around and finding something I didn't even know existed and would've never thought to look for. But that's about all they're good for. When I'm actually looking for something, they're usually a failure. 9/10 it's available on a pirate site though.