... Garmin (who are being beaten senseless by the smart phone apps)...
Well, if you need it so much, and you think others do, learn how to code and write it.You seem to think there's a ready made market. I would probably make it Open Source and give it away for free and have others join in, but you can try selling it if you want. I'd suggest Android as the target OS.
"Too expensive" is the obvious answer.
Since none of their programming staff is currently working in Basecamp (as far as we can tell), they must be working on other stuff. So, no, they don't appear to have the staff.
A "from scratch redo" (you make it sound much easier than it is) could be a two year project for a group of 4 people. And, they might have to write two versions (one for Windows; one for MacOS). (It's roughly, a $2 million dollar project.)
For something (currently, free) that returns no direct revenue. And to replace a program that works reasonably-well for most of its current users.
Probably, only a small percentage of Garmin users use Basecamp (a few RV-ers, motorcyclists, and hikers, for the most part).
If you go hiking, which is a well established world wide market, you cant use a web connected device. There is little, if any service. So the device must be stand alone.
The recent addition of sat phone service shows these devices are made to be used where there is no service.
It cost A LOT more to make a new hardware product then make a software. The software can also be used on many devices over a decade.
Your argument assumes Garmin has no idea what they are doing.
It seems more likely that Garmin understands how their market works better than you (or I).
City Nav NT has been correct so many times with a cab driver is using apple or some andriod app or even google. City Nav NV is really good. I see it in action against other things all the time.
It's fine that you want Basecamp to be improved but realize that you are using it in a rather extreme manner.