What was the attack surface of the jails/zones? I don't think the distinction here is startup vs. large company but internal vs. external. We used jails at my last company as a last line of defense (and, full disclosure, I wrote about 100 lines of code to use unshare(1) etc. when that machine was our last FreeBSD box remaining in our Linux conversion), but it was on a non-internet-accessible server where the jailed network connection was routed only to a single other (much larger) business that we had an established relationship with. If attacker code were executing inside the jail, there was already a serious breach.

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.