People are generally jealous. Docker feels small enough that "anyone could code it over the weekend", and so they think there is no way this is worth so much money. Of course nobody is trying to actually code something like this over the weekend, or once they do they just shut up.

The cognitive dissonance and entitlement with some is just funny to watch. They have no problem buying stuff from billion dollar companies who treat workers as crap and don't pay taxes, but a smaller developer wants to make money off of their hard work? Nah...

It's probably because a good chunk of the community is composed of privileged people, who never experienced the struggle.