The problem is that the system is unsustainable in the long term. There will always be new primes being introduced, but they only have a few out at a time, which means there will always be fewer and fewer opportunities to get all of them as more primes stay vaulted for longer. The fact that certain primes are repeated constantly and others are ignored just boosts this trend.
At least they're being transparent about the fact that artificial scarcity IS their business model. And it's worked for years. But can it be sustained?