This looks to me like a reprise of the systemd situation.
Someone has a bright idea and starts getting people on board. Then, ambition starts making itself felt, and the project starts spreading, taking in new areas and methods thus alienating some of the original supporters.
I'm not sure why this should be, not being a developer, but the lure of the new and as I said ambition seem to promote "mission creep" and bloat. Not knowing when to stop does seem to be a problem with both these projects.
With luck the Docker people will be more amenable to outside suggestions and constructive criticism otherwise I can foresee another promising technology becoming bogged down in argument and recrimination.
It does seem to as if the developers of both projects have forgotten the Unix way of working. Write a program to do one thing and do it well, and not try to be all things to all men.