As someone who uses GrapheneOS with Sandboxed Google Play for nearly a year now, I am struggling to think about why one would not be able to use it as their daily driver. It has all the features of a regular Pixel phone, except with more security. And the security features are not even some high-level enthusiast stuff, it is (among others) some really basic features like restricting internet access for specific apps or only giving apps read permission for specific folders on your phone instead of everything. Basic security and privacy features that every device should have.

My thoughts as a layman:

They probably have very different rulesets. Deaflympics “only” has to account for the fact that the athletes cannot hear sounds like speaker announcements, starting pistols etc., whereas Paralympic athletes have physical disabilities that directly influence their performance.