Because Elon has continuously misrepresented this:
The data used for flight-tracking accounts like ElonJet - called ADS-B data - are transmitted from nearly every plane in the sky.
The signals are unencrypted, and anyone with a $20 RTL-SDR radio can pick them up. Aviation hobbyists gather the data and put them on websites like ADS-B Exchange.
It's publicly available, legally acquired data of the kind Elon Musk said he'd allow, until suddenly he no longer did.