> how often do you really want to explore the docs in a specific version?

All the time. It's inevitable. If you ever sell software in the tools / configuration / package management space to "the enterprise" (which I think you do) then some of your biggest customers are going to be stuck on old versions. They'll need to easily select the version they're running if only to figure out how to upgrade to the version you want them to be running.

Edit: To clarify and drive the point home, in a previous life I was at a startup that sold something like Glasskube to enterprises. Version 3 of our software was significantly more performant and had some desirable features compared to version 2. Many of our largest paying customers literally called us up and asked us for help upgrading them. In that situation it was invaluable for our own CEO and pro services team to pull up version 2 docs side-by-side with version 3 docs, pull up a copy of the customer's code, then plan the migration for them step by step. This resulted in both revenue from the professional services and revenue from the license expansion as the customer scaled out on version 3.

So, versioned docs aren't just for customers, they're also for you, your developers (who may need to patch an old version or develop a migration tool), and your service delivery team.