Quite simply, we don't have them on every truck when I was still working EMS. IIRC, out of 9 trucks in the system, we purchased two, and they were given to the two supervisors (who responded on all cardiac arrests, but never beat the ambulance to the scene). So their real world use was pretty limited.
They look awesome, they are expensive, and they are new to EMS. And it should increase success rates.
But like many things in EMS, the old school will push back "we didn't need those fancy things to intubate back in the day," the new school will like them but not want to be seen as requiring a crutch to do the job (at least that is what they will hear from their FTOs), and if they aren't maintained by administration, and technologically updated as needed, the field personnel's view of them will not be positive.