Wait, you were only having problems with peeps not buying priority passes? I thought you meant all shoips
Priority passes only sell under the following circumstances:
1. Most rides in the park, especially most of the popular rides with long normal queues, have priority queues.
2. The priority pass isn't prohibitively expensive.
3. The specific peep involved thinks it's a good value. Not many do, and that number depends not only on the above factors but also on the price of the pass in relation to the price of everything else in the park. The more attractive the priority pass, the more you'll sell.
But you really don't want to sell TOO many priority passes. After all, the priority pass usually lets you get in a shortcut queue to cut ahead of the unwashed masses. Thus, no ride can have very many peeps waiting in the priority queue. So for instance, if your priority queue floor space is about 10% of the length of the main queue, you don't want to sell priority passes to more than about 10% of your customers. Another reason to not want to sell too many priority passes is that the "proletariat" waiting in the main queue, either too poor or too proud to buy a priority pass, get slightly resentful when the "bourgeois" with passes cut ahead of them and the more that happens, the less happy they become with the park in general.
Bottom line, priority passes aren't a way to make big money. The minority of peeps who buy them are quite happy, often enough to hit an ATM to spend more, and have more time to spend it because they don't wait in line so long. But this doesn't add up to a lot of money, especially after you pay the vendor(s) to sell the passes. Plus, it costs money up front to build the priority queues in addition to the regular queues, plus the larger building to cover them both. And at the same time, the majority of your customers don't like the whole concept so are grumpier.