I think you are right to some extent, but also I think the way you are used to think is biased by living with that perverted market model for a long time.
Here are a few statements:
1) Garmin could easily allow making trial map licences, so anyone could try any map for any period of time. They could also allow selling time-limited licences for lower prices. It's because GPS devices have a reliable source of time, GPS signal.
2) When there are many map producers, both small and large, there are more free competition, so the prices are lower.
3) Don't you think that the map prices are so high partly because map producers are already taking into account losses due to piracy. It's true at least for the former CIS countries.
4) I don't know how things are going in other countries, but in the former CIS piracy really rules. I've never met anyone who buys maps legally.
One wise man told me that Garmin is quite conservative and don't want to make dangerous steps in order to drink even more champaign later. That's why I'm pretty sure the situation is not going to change soon.