If I remember rightly from previous threads I think this is a WAV that was returned nearly new. I think it being a WAV is a big factor in this decision.
As the owners of the vehicles and administrators of the scheme I imagine Motability have the freedom to make exceptions to their own rules if they choose to.
It sounds to me that the dealer has decided to re-register the car by post rather than going to a post office or DVLA office. Like many government departments they are dealing with backlogs post pandemic and this may be delaying the registration.
As stated by others, the customer is the registered keeper (has to be for the purpose of parking or traffic violations) but Motability are the registered owner and hold the V5.
If I seem a little strange, that's because I am.
Skoda Karoq SEL.