> Docker’s journey reads like a startup trying to find product-market fit, except Docker already had product-market fit

Strongly disagree. The core Docker technology was an excellent product and as the article says, had a massive impact on the industry. But they never found a market for that technology at any price point that wasn't ~free, so they didn't have PMF. That technology also only took off in the way it did because it was free and open source.

The entire technology is a wrapper on setns().