Firstly, It's not refuse, it's decline.
Decades ago, the old head paramedics told me they had about a 50% no-load rate and still felt they were a taxi service.
With today's telemedicine capabilities, appropriate supervision , working guidelines, and quality control feedback, a huge reduction in transport can be achieved safely.
"Price is no object if you have no intention of paying," People value something more when they have to pay for it. The old Charity Hospital in New Orleans was locally known as "The Big Free". EMS systems are the same. Make people pay-something (or deduct it from welfare benefits). Make it regressive. Starting from zero- the less the emergency, the more you pay.
The other issue; cities have EMS billing offices. Medicare, Medicaid, and private insurance (health or liability) may pay for ambulance transport. I think the charge is around $1500. While the engine company is sound asleep upstairs, the medics can be generating potential income for the city fathers.
Hospitals have the same incentives. Whenever an EMS unit brings an unnecessary transport to a local ER, the hospital has to do two things; render care and generate a bill as noted above. Plus, hospitals that take care of a lot of non-paying customers get a special disproportionate (known as "dispro") payments from the state.