I am puzzled by this. Our GSHP does not require any annual maintenance so what do these HVAC companies do? I assume the air filter is on some kind of forced air ducting system, which we don't have, and changing that filter is a maintenance overhead on the heat distribution system, not the GSHP, and that cost applies reardless of the heat source.
We would certainly not have installed our GSHP if we thought it would have such a short life. We installed ours in 2007 and I expect it to go on for a good few years yet.
Figure that the mechanical systems companies set up here cleaned oil furnaces (which were dominant) once a year. That gave them a chance to come, clean the furnace, touch base with the customer, etc. They get revenue stream from that and they don't want to give it up. They suggest looking at a gas furnace and A/C here every year if you ask them, but they're looking to collect $185 or something to just browse over stuff with a flash light and they're also looking for work. When there's a heat exchanger involved, there is one safety issue there - that the exchanger is cracked and the breach allows CO into the ducted system.
For the GSHP, I asked my FIL what they did for $279 the first year and he said "not much". There's some kind of exotic air filter in the system that probably costs a mint, but other than that, they're just looking through it. If you are willing to keep paying them, they will keep coming.
I don't call them except once in a great while - why? because if the system needs replacing or there are issues, most of them I will notice (I am lucky to have a furnace design at this point that will flicker the flame in a visible way when the fan comes on if any significant heat exchanger breach...so I check it once or twice a year when it comes on). Other than that, by the time you roll $4k into 20 years of "inspections", you can buy another unit. I'll just buy another unit when it needs replacing.
I haven't asked FIL about this - he convinced the oil furnace service man in his prior home to show him what he was doing and describe the tools, and then he cleaned the boiler tubes and remainder of the furnace each year instead of hiring it done. I'm sure he's cut back to some extent with the GSHP.
I don't remember the quotes for system life - something like 50 years for the ground bits, but I can't remember exactly what they said about the heat pump other that "they will last a lot longer than the older ones did".
Forced air has become the standard here by a long way as I'm guessing that flexible ducting is installed in new homes (so no tinner to pay, and no tin to buy). Most of the home products seem to have two aims - take the cost of materials out, and take the skill out. If both of those aren't met, then most products don't get wide adoption).
When I see planned communites in the US on slabs like "the villages" and the houses are $350K for 2k square feet above ground and they're frame/drywall/roof/tons of MDF trim, and modular kitchen and bath products, I don't really get there the cost is in them, but I guess that's the point.