I was trying to change my primary YouTube/Google account while still holding onto my Movies & TV purchases.

1. You can't change the email address associated with your YouTube account or Google Play Movies & TV purchases.
2. You can't transfer your purchases to a new Google account.
3. There is a way to create a Google Play family account, but it's so buried and un-obvious that it takes search engine research to accidentally discover that this is an option.
4. Once you create your family account, apparently some purchases can't be shared due to how they were paid for years ago.
5. When you try to share many stated-as-"eligible" purchases with the family by using the toggle, it errors, and a refresh shows that it never shared. I used Firefox, Edge, no VPN, and no adblocker. Tons of attempts. Nothing. No fix.
6. Google has no proper support channel.
7. If you try to remove the family account and host it under the Google account that owns all the purchases in hopes that they will now work, you will discover that none of the accounts can join a family plan again for 12 fucking months.

Lesson: Don't ever buy your shit through Google Play. Put your pirate hat on.