My friend, I struggled with this too at first, but there's a possibility that this decision was made jointly with the player, essentially following a "keep catching" path which has helped Cooper Hummel and David Fry make the big leagues.
In Nashville, you have to figure that the catching starts will be 4 games Quero, 2 games Navarreto each week. Quero needs the experience and Navarreto needs to stay fresh. Then Coach Murphy or another senior coach mentioned that Black should play 4 days at first base and 2 days at third base. So Clarke would basically have been left with 1-2 first base starts and 2-3 DH starts per week.
Wes Clarke has been listed as the starting catcher in 7 Minor League Spring Training games thus far (vs. Wood 5, Kahle 4, Norman 3, Diaz 3, Navarreto 2, Yerzy 2, D. Garcia 2, Quero 1, D. Miller 1, R. Rodriguez 1). As such, I'm guessing Wes will get at least 3 starts behind the plate in Biloxi per week, paired up with 2 players amongst Ramon Rodriguez, David Garcia, Andy Yerzy or Nick Kahle.