I think the issue there is that once you start building a number of containers, it's easy to start noticing patterns that repeats across your containers, and so it's very tempting to do what you mention to avoid repeating yourself.

I sort of agree with you, but I think it reflects a tooling problem in expanding dependencies more than anything.

After all, Docker introduces temporary images for nearly every step of the Docker file anyway, so if these "parent containers" are genuine dependencies it's beneficial to collapse the steps for individual app containers down to a set of shared ancestors as possible.