To be absolutely clear about this, the digikam developers have no
control over when a particular Linux distribution includes or updates
digikam (or any other program such as GIMP) in their distribution.
So please do not take your difficulty in getting the very latest version
of digikam working on an older version of a distribution to be in any
way a reflection of the dedication and hard work put in by the digikam
developers.
Linux distributions are a tested collection of programs and libraries
that should all work well together. Once you update a part of that
distribution you are departing from that tested collection. Different
Linux distributions have varying support for allowing this.
Andrew