I read some more on this topic and found out something Interesting from a former race Tyre Tech on a british racing website.
He claims it is to help keep the tyre in good condition for the tyre techs to check the tyre performance and wear, If the Tyre is allowed to cool to quickly it can damage the carcass and the rubber and will not give the information that is required for the tyre specialists, So they are allowed to cover one tyre in Parc Ferme (front or rear), The tyre techs used to be allowed to take readings from the tyre straight after the race (Temp and wear), Now they are not allowed to touch any part of the Bike or Tyre except to cover it, Each team is only allowed 2 nominated assistants in the Parc ferme area at race end to assist the rider, cover the tire and place the bike on a stand.
If the nominated Assistants are seen touching controls, displays or adjustments (other than to switch off the bike) the Team and rider will be instantly disqualified.
And apparently hiding the tyre from there competitors is not a high priority because as the racer comes back into the pits the tyre collects a large amount of debris and rubbish from the track and pit lane, so a lot of wear on the tyre can not be seen until the tyre is cleaned for final inspection.
Hope this helps.