I also think the cost of formula gear causes many to stay away as well as the perception that the "giant" sails are impossible to manage. If you get comfortable with 6 and 7 meter sails as your largest, the 11 & 12 meters sails do seem "giant" and hard to manage. However, once your skill level gets to the point of rarely dropping the sail, staying powered and balance while hooked in is pretty comfortable.
While I only race formula a couple of times a year, I will likely stick with the gear simply because it is wonderful to be planing relatively fast in 10-15 knots of wind when most windsurfers are still at home.
My first choice for fun windsurfing is my bump and jump board in 20+ knots. Second is my iS slalom board in 12-20 knots, then formula in 8-15 knots.
Formula isn't for everyone, but some will find it fun and exhilarating. One side benefit is that after a session on a 9 or 11 meter sail, dropping down to a 7.6 on a slalom board feels like you have a napkin in your hands.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.