Why the Blues are in civilian clothes when they arrive at Clairefontaine

Among the Blues, no explicit element specifies the moment from which players are required to wear the Nike outfit. It is customary for them to arrive “in civilian clothes” before recovering their official outfits once inside the castle. If no discussion on the subject has taken place to date, would a change in the rules be possible? Also dressed by Nike (until 2030), the English are, for example, required to wear the official uniform of the Three Lions upon their arrival at St George’s Park, their training center. So much the worse for fashion lovers.