Are you talking about the girls on a specific team you coach or is this a general observation you have made accross a number of teams and ages?
I'll give you my observations from the perspective of a coach that runs a school exclusively for catchers and we see catchers from all over the country. All year long when a new clinic begins I always asked the kids why they got started catching. By far the most common answer, even with young 8 yr olds, was "If you catch you get to play 6 innings" . The 2nd answer is "I don't get bored back there since I am in every play"
Not sure what coaches are doing to get them to catch, I obviously see them after they have gotten hooked on the position. But those answers may help steer your "marketing efforts"
In hopes of finding the girl that likes it after she tries it I suggest the "Catching by Committee" theory. Have the girls rotate and have each girl give it a try for just an inning a game.
That way no one feels like they have been "sentenced" to a life of pain and misery back there. This way they learn another lesson about teamwork and you may find that girl that realizes when she is back there that she is involved in every play....no time to dig holes like in the outfield.
We ran into this 7 years back when my pitching daughter was playing rec. There were two athletes on the team, mine and one other kid. I asked for catchers, no one volunteered. My kid said 'hey, Dad I;ll catch, looks like fun." I said, fine, but who will pitch. Athlete #2, said 'teach me and I will'. So I worked with Athlete #2, then I went and bought a brand new set of nice catchers gear, athlete #2 got to the point of being "game-able" - she had been working at home, copying my kid. Next game, my kid caught, Athlete #2 pitched, and the other 8 girls all volunteered to learn how to catch. We ended up the season trading off, my kid would pitch 3 innings, and then catch 3 innings, athlete #2 would catch 3 and then pitch 3. We would get ahead and some of the other 8 girls would get a shot at catching.
Rotation is what we have done in rec ball, but with the younger kids U9 we have done this with every position.
A girl may have decided she wants to play 3B, but on my team she's going to get to play every position (but not in every game). This is important for their growth and learning the game a well . That said, it's equally important for me as coach to learn in what areas the kids have strengths/weaknesses and to have flexibility on the days that someone has a dance recital, etc.
As they get older, I still try to move them around a bit so by the time they are 12 they feel comfortable in 3 or more positions (one of which being OF).
In one of the last games last year we found out a girl who had been playing around all season was actually a fantastic catcher. It turns out she was too shy to ask to try it, but when she got her chance we and she learned that she was a natural.
In addition to the rotation idea to find out who might like it, some of the concepts I've used/emphasized when trying to get girls excited about the position as they have rotated...
Uniqueness of the position...only player to face the other direction and see everything. It provides them with a unique perspective and viewpoint of the game. Only position, other than pitcher, involved in every play.
Importance of the position...I've seen many games won/lost by poor performance at this position. Unfortunately, many rec leagues for fastpitch have been modified (no stealing or no scoring on WP/PB) so as to take out some of the critical nature of the position, but this varies. Certainly, in travel ball and HS, this is a position where you want one of your better athletes and game savvy players.
Quarterback of the defensive team...due in large part to their visual perspective of the game, catchers are in a better position to provide direction to other fielders for game situations.
Display a passion for the position...this has worked well for me for the girls teams that I have coached, particularly at the younger ages. This can be done through the points above AND by singling out the catchers during practice for their own drills just like every other position. Not only will you develop better catchers by doing this, it will emphasize, through actions, the importance of the position. Coach Weaver's website has a lot of good stuff on it in this regard.