Not to mention each of the studio streaming services will suck compared to the one created by a company living and dying on the streaming itself.
Oh, and I haven't even mentioned DRM. The studios have demonstrated a certain inability to judge the DRM tradeoffs when left to their own devices. Maybe the studios could get away with running their own download-of-not-DRMed-files, but if they've also got to create their own DRM and make it work on all the rapidly-multiplying number of streaming devices out there, it'll be even worse. TVs that can receive ABC but not CBS... hooray for the 21st century!
They may try... I don't deny they may try. But it won't go well.