(from a technical perspective, you would be running jails for years too - so much about platform loyality)
Jails haven't been used to protect as many high-value targets as Linux containers have. This is not a comment on the technical quality of jails. It may well be a comment on the world's anti-FreeBSD prejudice. But either way it's still true, and that means the 19 years of existence didn't magically harden the product.
This is not true in my experience at all. It may be true that it hasn't been in use at startups until Docker came out, but a few large, established companies I've worked at absolutely used Jails or Zones to protect their most valuable IP. And have been for a long time.
The distinction here is that people are running containers in the cloud and also often running untrusted code (e.g. vendor software, random exciting open-source things) inside containers, and collocating those with high-value targets in other containers. And large, established companies are doing that now just as much as startups are.