I was also wondering, best I can find is from this reddit comment:

Koontz was never on King's level as a writer, so King would never have been threatened by him.

Dean Koontz comes up a lot with King fans because they wrote similar stuff at one point. Dean Koontz went through many phases, and during one, he wrote a bunch of government conspiracy stuff — I strongly recommend The House of Thunder — which was similar to what King did with Firestarter and a couple others. So at that time, in the 1980s, they were doing the same thing. Since then, however, both authors took separate paths.