Debian is popular for Docker images exactly because many of the people trying Docker were already familiar with Ubuntu. Those users quickly ended up wanting smaller images, making Debian an obvious thing to try out since Ubuntu is basically Debian with bells on.
Ubuntu fought a sea of distros and came out as what's very nearly an industry standard, if not an official one. The 90s were a fricking mess by comparison. Slackware on floppies.
(And now I need "Slackware on floppies" dubbed over the "Jesus wept" scene from Hellraiser.)
I think you may be living in a bubble. I've been running devops for various shops for half a decade and I've only once used Ubuntu, because it was already being used by an acquisition.
I won't deny that Ubuntu is popular. It's certainly got the lions share of the desktop market. But there is no such consensus in the server market.
Here's some date I could dig up by a couple of minutes googling:
https://w3techs.com/technologies/details/os-linux/all/all https://w3techs.com/technologies/history_details/os-linux
Other sibling comments link to more.
make menuconfig
Here's a report that suggests the exact opposite:
"Don't let the revenue numbers lead you to thinking Red Hat Enterprise Linux (RHEL) is more popular than Ubuntu. By The Cloud Market's Jan. 8, 2019 count of Amazon Web Services (AWS) instances, Ubuntu is used in 314,492 instances, more than any other operating system, while RHEL is used in 22,072 instances."
https://www.zdnet.com/article/inside-ubuntus-financials/
Disclosure: I work for Canonical, but as an engineer; I'm not in marketing or anything and that's not my job. But I do get the impression that Ubuntu is way ahead in general use in the cloud, and is also the generally used base for Docker images (I don't immediately see how to get that statistic out of Docker Hub). I didn't think this statement was controversial.
The last data seems to be about 3 years old, and Ubuntu was about 1.5-2x the CentOS/amazon linux share. I suspect that's changing with the release of amazon linux 2, but there's no data to back that up.
Amazon itself primarily uses a RHEL based distro, which is what I meant originally.
It's always like this.
Think how Ubuntu took over the server market because amateurs were preferring it instead of Redhat/CentOS. And when they became professionals or were in a position to decide, they also put Ubuntu on the server because this is what they knew best.