I work for a Bluetooth chip manufacturer and agree with you 100%. The big problem is that there are too many luddites that think that anything digital must be unreliable, and wouldn't buy it. The more electronics and the less mechanical the better as far as I am concerned.
Maybe I picked the wrong example
Bluetooth (which I have used widely) is reliable in common retail stuff like phones/headsets and flakey in much other stuff. The devices get debugged where there is the strong commercial incentive to do so, and low volume stuff is often never fixed. Someone like Garmin could put resources into developing / incorporating a bluetooth radio into a unit of theirs. They would have to be careful though - the problem is that one is then left with a wide variety of laptops, with their various crappy bluetooth stacks. I think they would have to specify compatible laptops and specific bluetooth driver versions on them which are known to work, and everything else is unsupported (the de facto situation in IT).
I think the issue is certification, and this involves validating the input data, which with a bluetooth radio connecting to potentially anything within range would probably be impossible. That I am sure is why Jepp/Garmin have gone the "text file on a flash cartridge" route, because the validation of such data can be done to very narrow criteria.
No criticism meant, a genuine question - what advantage is there to this software, over simply inputting a flightplan manually on the day?
Purely the time.
Take an FL100 airways flight plan
EGMD LYD DCT KONAN L607 RUDUS L984 ASKIK Z74 KOSEK L603 OBEDI/N0150F150 L172 VIW/N0150F140 L608 DOL P173 KOMAR L187 DBK R45 RODON N732 PITAS
LGKR
Most GPSs cannot take the airway names, so you have to put in the waypoints and my waypoint count for the above route is 59, most of which are 5-character names. I could paste them all here but won't
Enetering this lot into the GPS, with its 2-knob user interface, takes quite a while. A lot of the time one departs while a 2nd pilot enters them in... not ideal. Not something I fancy doing single-pilot, in turbulence