The fee is the problem. They need to lower the fee AND enforce the existing rules.
The fee is the problem! Maybe if the airlines stop to charge the fee, or charge a small and reasonable fee, people will stop with this nonsense.
A doctor's letter costs about US$150, and it is valid for one year.
A pet transportation fee is about the same price, but for only one leg. If the carriers start to charge something like US$50 for round trip, for the eventual traveler may be cheaper to pay the fee instead of the doctor.
I know it won't solve the problem for large pets, but at least part of the problem will be fixed.