I stand corrected on that one, however it was then another piece of the stack they ended up losing as added value.

The spinning out of containerd is best understood in combination with the launch of Docker Desktop, which was not open source, and later became the main source of revenue.

Docker in its entirety was at risk of being wrapped as a commodity component. By spinning out lower-level components under a different brand, they (we) made it possible to keep control of the Docker brand, and use it to sell value-added products.

Source: I'm the founder of Docker.