They (sort of) are! It gets into the nuance of the weather model side of things, which I don't know as much about, but the HRRR/ GFS models ingest data from APRS and incorporate that into their forecasts. This means that these observations are included (especially in the US), but are at about a 2 hour lag compared to direct readings
Right now there are thousands of weather stations posting regular reports via APRS.
Any chance to see those integrated?