Because they are gay. From reading, and having the unfortunate experience of seeing one of these Masses, 90% of the "priests" who do this are homosexuals, many of who are active homosexuals.

The priest in my college days 12 years ago who dressed up like a clown, complete with ruffled collar and yellow hair was a few months later accused of sexual abuse of two Freshmen who in good faith had volunterred to help in the liturgical office on campus. Little did they know what they were getting themselves involved with. Sick stuff, sick, utterly sick and depraved priests. Typical Vatican II clergy. Sometimes the priests dress up as clowns in parishes for Mass...but it's often the radical habitless femminist lesbian nuns on staff who actually plan the liturgies.