The real problem was the downright hostility towards everyone outside of Docker... with shykes (Solomon Hykes) leading the belligerent charge on the community at large. The countless arguments shykes got into with potential users right here on HN, and all the new fake accounts that would suddenly crop up to defend his positions. It was transparently an attempt to wield HN as a weapon against anyone that questioned what Docker was doing.

Starting with the outright lies about what Docker could or could not do (Docker does X, Y, and Z - but Y and Z were actually still in development), to the outright refusal to play nice with the open source community (remember the Docker vs. CoreOS fights for standardization of container formats?). If Docker didn't invent it, or think of it first, it was a terrible idea and had to die.

They even went so far as to start a convention before they had a production product.

Then Kubernetes, Rocket and all the other container platforms and tooling came along and ate their lunch. Why did people adopt them so quickly? Because they played nice with each other and made it easy to build your system as you wanted it... not just as Docker wanted it.

The entire thing was a money grab. And when things went sideways, they made some terrible decisions (the entire Moby fiasco). It's not surprising Docker finally fell...