I'm not sure what you mean by "never took off" but thousands of developers around the world, myself included, have made their living just writing Clojure code for many years. So, it has certainly taken off for them. And there are many, many companies using it all over the world. I live in a town of about half a million people, so not super big, and there are about 12 companies primarily operating on a Clojure codebase.
Amazon also uses Fortran, Assembly, Awk, Mosel, VBA, K, and Bash, but nobody is going around claiming they have much usage on real world projects.
Walmart is using Clojure for their checkouts as well https://www.youtube.com/watch?v=av9Xi6CNqq4
Boeing is using it in the onboard control systems for the 737 Max https://www.youtube.com/watch?v=iUC7noGU1mQ
It's not some obscure microservice that some intern wrote over the weekend, these companies are using the language for critical applications, and the feedback from these companies is positive.
If anybody led you to believe that their team did “online checkout”, but didn’t care to explain how small of a cog they were in an extremely complex system composed of hundreds of services, then you were grossly misled.
If someone doesn't want to use it for this reason or that, it's their loss not ours. Those who need to find Clojure eventually will, because there is nothing else like it.
You wouldn't want Clojure, Java or any languauge with GC running in a pacemaker either. Those are all also very important distinctions.
C++ actually proved difficult to adopt over C. The language is too difficult and the tooling is too poor. It's too hard to run a static analysis or prove 100% code coverage.
With regards to tooling, the windows visual studio experience for C++ is widely counted as one of the best development setups in the industry for any language. I know lots of people working in other languages that envy what C++ developers get.
Clojure never had much usage on real world projects. It cannot be extinguishes as it never took of.