The difficulties with on-board W&CG systems are straightforward enough, although perhaps not quite so simple to solve - a quick back-of-envelope sum suggests that you might get around ±5% weight error due to surface wind, and perhaps ±2% in CG position. That is an error too gross to be acceptable.
So, to cope with that you'd need a stack of wind tunnel data for the aircraft in ground effect showing effects of winds from various vectors, PLUS some kind of accurate windspeed instrumentation, PLUS you'd have to have the aircraft sat well clear of any rotor over buildings or other factors that would make the airflow over the parked aircraft unpredictable. This would basically mean taxiing it to the hold before you knew if you were accurately in W&CG limits! (And at some fields, that wouldn't be reliable either).
On the other hand, you can simply try and maintain a reasonable control and monitor over the loading of an aircraft. This aint complicated, it just requires to you weigh everything that goes on board and do some maths that my stepson, who failed his maths GCSE, could just about cope with - and in any case can be easily computerised.
Sorry, my money's on loadsheets.
G