Someone had to make them. Just because they were bootstrapped does not mean they were free. You have to value your time at something.

That said, you are right, there are some success stories that don't have huge budgets. The article does attempt to address this though:

It’s easy to look at outlier examples such as the early Facebook apps and think that those games are normal examples of where dedication can get you, but you’re failing to take account of context if you do that. Very early adopters in a brand new market can afford to get away with appalling levels of production because the market is so new that there are no expectations. Most games are not developed for brand new markets.