The same can be seen on sites like HUnqz or boys4u-where in EUR guys advertise their services. The reason is daft simple, IMHO: they want to show its safe to visit them as they take precautions and hence will not infect you. here many also proudly state they have been vaccinated twice.
Just try if you still get enough response posing without a MNC=mouth nose cover?
But it would be interesting to check which would offer more response-just make a comparison with 2 accounts?!