I believe Zecco's business model was "We'll just remove our marketing budget so you can pay $4.95 per trade", which isn't unsustainable, but their merger with TradeKing shows that they probably didn't execute it as well as they could have.
That was later. They started off with $zero commissions (I believe this was the inspiration for the name Zecco). It started as no commissions no matter the account size, then they added minimums which crept up for a while, then, as I recall, they removed free commissions entirely, then they were bought by TradeKing.
Yeah, I was a member way back in the day (like 2006 I believe). It started off as free trades, then it was only 25 free trades a month, then it moved to $4.95, then they were sold to TradeKing. Similar thing with ThinkorSwim, they were also bought out. Perhaps RobinHood's strategy is to just acquire users at a loss and then get bought out...