I assume the girls are the equivalent of "Grid Girls" in Formula One racing, I. E. they hang around to give the spectators something to look at when there are no vehicles around.
Of course, in spite of the name, the Isle of Man has always had a lot of girls on it, as English music hall star George Formby noticed 80 years ago:
Here's another shot of girls, once again, all of the same race, on the Isle of Man.
The lovely @MonsterEnergy Girls at the Isle Of Man TT! pic.twitter.com/xcH3AFbvQ8
— Monster Energy (@MonsterEnergy) June 5, 2013
And here's the song Formby wrote 80 years ago for a movie about the races: