I can think of a few reasons...
1) It takes up space on their servers.
2) They have to program for the extra data.
3) The software providers that support WU uploads would have to program for it.
4) All those people then have to support that ability for something that...
5) is of no interest to anyone else except the person running the weather station.
and WU is "free" so all that programming and server space has to be paid for by their other services.
This is a good reason why some of us build our own sites. On SLOweather.com I have a graphs page for several extra Davis sensors, including our spa temperature, the temperature and humidity down in the woods, and the temperature in the greenhouse.
Even VWS doesn't read and graph all the possible extra Davis sensors. It frustrated me to learn that I can't display soil moisture and leaf wetness with it.
If you run your own site, there's a script you can use that will generate your own weather stamp with whatever data on it you want.
OTOH, we're programming WeatherElement from the ground up to save and display dang near everything we can suck out of the console. That includes indoor temp and humidity, the console battery voltage, all of the extra wireless sensors, and the battery statuses from any extra wireless sensors.
Heh, we can even control the console back light remotely and set the console clock.
But, WeatherElement won't be free, either...
