Sometime at the end of August, Elecraft quietly flagged the K1 and KX1 rigs as "discontinued"

Once the word started going around and people asked questions, the following was posted to the Elecraft reflector on QTH.NET by Elecraft's Wayne Burdick N6KR, specifically referring to the K1:
We should have made a formal announcement here. Yes, we discontinued it because certain parts are hard to come by now, making it no longer cost effective for us to manufacture.

It was a great product for us, and I used mine for years, taking it on many trips. I thought of it as a “Sierra on Steroids” at the time (referring to an earlier design I did for the NorCal QRP Club). But we’ve moved on to more versatile field radios, including the KX2 and KX3.

73, Wayne N6KR

There have been reports on various reflectors and websites of late that certain K1 accessories were no longer available due to the lack of parts, and there have been posts referring to issues with boards containing newer SMD components that were now too small to fit on the original boards, so this bound to happen.

Nothing specific as of yet as to why the KX1 is now discontinued.