Originally he believed that we had a well-functioning free market, and that everything that got built was just the market expressing consumer preferences. Over time he (and I and many others) began to realize that the system was not a functioning free-market at all, but rather a strange amalgam of layers of public policy and social engineering with really bad side effects.
This isn’t super easy to see because it’s hidden in a bunch of cultural stuff we just take for granted. Things like how so many postwar neighborhood have 40’ wide paved streets with curb and gutter, sewer, and buried utilities. That must be because it’s practical and affordable, right? But when you really dig into it you find that the homes lining that street don’t even pay a meaningful fraction of the maintenance cost of that infrastructure... so where does the money come from? That turns out to be very opaque and hard to answer. (You can read about it here: https://www.strongtowns.org/the-growth-ponzi-scheme)
And so on. So as we began to figure this stuff out, we built Strong Towns to share what we were finding and try and get a lot more people to look at it in their own communities so we could figure out how widespread these phenomena were, and start to figuring out what to do about it. That journey is still in progress.