Earlier quoted context omitted.
it's likely dumber than that: bait and switch. Facebook had done this before: they gave third parties rich access to their data via Graph API, which in turn helped Facebook to grow. Once their social graph growth phase began to slow down, Facebook severely cut off data access.
I have an Oculus Quest 1. How are they going to update it to stop supporting sideloading when they've stopped supporting it officially altogether?
1. Almost every VR device is not yet sold. It doesn't matter what you can do with existing devices because they are a tiny fraction of the market.
2. Devices are going to improve drastically. No one is going to be using a VR device from today except as a retro computing device anyways.