It was an impression of mine, but it seems it was just bias of availability because I heard some bootcamps were changing Rails for Python.
But I believe I was wrong on this one. A quick search on a page I googled for "best coding bootcamps" led me to this page[0] where a quick ctrl-f showed the results: Ruby = 34 results, Node = 18, Python = 12.
[0] https://www.switchup.org/research/best-coding-bootcamps