Its not that there is no understanding of the potential benefits, but ...
Its not so simple as saying it, there have been several attempts to make it happen.
But they require a _lot_ of work because lots of the existing code simply wasn't written to allow for more than one pane (which is why much of it doesn't work in the second pane) or they have limitations (like the current plugin) or they have performance problems (like the switch pane implementation).
So none has been good enough to displace the limited existing limited plugin. Perhaps it should be made read-only and documented as such, but nobody has felt its worth cutting off the limited functionality it has.
Probably the existing plugin could use better documentation though. Actually any at all [its not mentioned in the manual](https://www.geany.org/manual/current/index.html#plugin-documentation).
Pull requests are welcome.