פירוש על מלכים א 2:28

And the report reached Yoav. The report of Dovid’s charge, that he had commanded to kill him, and he knew that Shlomo hated him.¹⁷That is why Yoav feared for his life. Alternatively, he heard of Adoniyahu’s death and of Evyosor’s banishment.—Radak

For Yoav had sided with Adoniyah, but he had not sided with Avsholom. At the end of the matter; however, he did seek to turn after him, but he was fearful that trace of Dovid[’s might] was still present.