Because they are cheap and one of the more difficult units to detect on Ka 35.5gHz, or K-band where their power outputs are very low.
Is it happenstance or a dislike of the brand?
Decatur Genesis II
* Signal Processing 32 bit Digital Signal Processing
* Speeds are computed and verified 100 times per second
* Accuracy +/- 1 MPH stationary, +/- 2 MPH moving
* Beam Width 12 Degrees nominal (Ka-band, K-band) and 18 Degrees X-band
* Power Output 10 mW - 15 mW (Ka-band), 5 mW - 10 mW (K-band), 10 mW - 25 mW (X band)
Through daily experience I can tell you they are as bad or worse than Kustom Talons to deal with.