My guess is that they’re offering early sales because they predict that the stock value will tank after the public offering, so this way there’s a slightly higher margin of profit for the current shareholders. If that’s correct then it’s completely scummy. (i.e. extremely typical for Reddit)
Another possibility is that they’re trying to “force” power users to be more cooperative towards the platform, by giving them a financial incentive to do so - “if you shit here you’ll be tanking your own shares”.