It was never really yours to begin with. Apple sold you a very limited license to enjoy their content at their convenience. They can revoke this privilege at any time and for any reason or no reason.
Regrettably when it comes to popular media there is no way to permanently buy a copy to access on a mobile device of your choice. The only way to do so is to buy a bluray, and it is not allowed to circumvent the copy protection to transfer it from there to the mobile device.
There isn’t really an option to buy buy instead of rent buy in many situations, so the blame falls squarely on the media companies for failing to provide reasonable options, not the customer for choosing the best option from a bad list.
It was never really yours to begin with. Apple sold you a very limited license to enjoy their content at their convenience. They can revoke this privilege at any time and for any reason or no reason.