Speculating here: I would be surprised if the commercial vendors of EDA software such as Altium or Cadence offered continuing support for older versions of their software. I think that if one were to complain about bugs or other issues, the complainer would be instructed to upgrade, thereby trading older issues for newer ones. (??)
It’s not commercial software in the usual sense of the word, but for a comparison, fedora linux has two maintained releases going on at the same time, and the “development” version for the next version.
For example, when fedora 35 is the latest stable, 34 receives updates.
When fedora 36 is released, 34 doesn’t receive updates anymore (possibly a short transition period?), but 35 does until 37 is released.
It is helpful from a user perspective, as it gives a smoother transition between versions, but some extra developer resources are needed, which might be in short supply for KiCad.