Well for one, it's about disruption and change. The creators are more than familiar with brokerage, and it shouldn't be a shocker that most brokers do not operate trades, it's mostly electronic.[1] If you're going to hold stocks for years, why not skimp on an $8 commission? If you make a purchase of 100 shares of $FB, it could save you at least $800 for that sale.
So the real question is, why not?
[1] https://www.youtube.com/watch?v=JwpQpFqzoAE