Google dropped support, Broadpwn (CVE-2017-9417) was released, and there are no blobs to fix it. This stops the device from meeting requirements in the Lineage Charter, thus it is dropped from official status.

Nexmon was working on it last I checked, but it's highly unlikely this device will get any of this backported and built for Android.

I confess I didn't think it was vulnerable to that. If it is the reason LineageOS dropped it, the drop was a long time coming (2019).