Not OP, but as someone using Ubuntu LTS releases on several systems, I can answer my reason: Having the latest & greatest release of all software available is neat, but sometimes the stability of knowing "nothing on my system changes in any significant way until I ask it to upgrade to the next LTS" is just more valuable.
My primary example is my work laptop: I use a fairly fixed set of tools and for the few places where I need up-to-date ones I can install them manually (they are often proprietary and/or not-quite established tools that aren't available in most distros anyway).
A similar situation exists on my primary homelab server: it's running Debian because all the "services" are running in docker containers anyway, so the primary job of the OS is to do its job and stay out of my way. Upgrading various system components at essentially random times runs counter to that goal.