Or due to how small a proportion the entry fee is for the all up cost of PBP, travel, equipment, accommodation before and after (maybe even during) lost earnings. Also there are various extras which some people may consider part of the cost and others not.
Those expenses aren't as significant if you're French, and live close to the route. Especially if you ride as a club, and share transport and support.
The danger with ramping up the expense is that it can deter those who have a retinue of possible volunteers, i.e. family and club-mates. There's a crossover point between a volunteer-based event, and a commercial event. That's why there's a step-change in pricing, as paid labour enters the equation.