I think it has a lot to do with marketing and hype.
The BSD community in general is anti-hype, vs. Docker having a for-profit company (dotCloud) behind it. Even it's first version's website looked nice, had a lot of pretty graphics.
It really does more than people think. Now, the following statement doesn't apply to Docker, but I've seen people with great technical understanding seen choosing totally messy toy projects, because they had a well designed website with pretty images and lots of marketing.
I mean to some degree this also works for Docker in the sense that I've seen people having totally wrong expectations on what Docker does.
It's just what good marketing does: Giving people the impression that something is magic.
The BSD communities always had both a strong no-hype stances. They didn't even have cool names, as they have now with bhyve, etc. They also had a strong "keep it simple" mindset, that counters the "there is magic behind it" effect. It is the sysadmin mindset of preferring boringness and no surprises.
The only other bigger open source project I know trying to be boring to some(!) degree is Go. But that only works, because you can always say "it's from Google" if you need to market it.
Of course there are others, but many of them are way less known.
The only other _somewhat_ new software that I can think of that was considered cool without there being a big hype machine and/or a company pushing it from the beginning is Redis. Out of the nowhere, I mean. Of course there is much cool stuff done by people that already have proven to do amazing things.
But I am sure other people can come up with way more.