This has to be one of the strangest complaints, along with shadow flipping, that's come out of the real-estate debacle here in Vancouver.
Builders need to achieve 100% or near 100% sell-through on units in a project. Doing that through a pre-sell is hard, so they've traditionally offered a small discount on pre-sells. Buyers have typically been ok with committing themselves to a pre-sell because of the discount. Everyone's needs are satisfied.
If a pre-sell buyer decides to flip the property immediately, what harm is there in that? Is it that you didn't get the discount? This has exactly no impact at all on the steady-state market price of property; it's just a matter of who the builder decides to give this small one-time discount to.
Worse, it's a distraction from the real reason that real estate has become so expensive in Vancouver and Toronto, which is foreign investment. The BC government imposed a foreign investor tax here and the market is now in a slow-motion collapse; I've been watching about 2 dozen detached houses on realtor.ca and none of them have sold. Some have already dropped their asking price by about 100k-200k and they're still on offer.
If you want a real solution to housing prices, kick out the foreign speculators.