Likutei Sichos Vol 10 p 88-91 Yaakov refuses to make a covenant with Avimelech, where his father and grandfather had both made one. Why? Page 88.

Yaakov’s Mita was whole as his mission was to engage the lower worlds. Thus, his Avoda was quite different from that of Avrohom and Yitzchok. Page 88-9.

Yaakov’s inyan personally is Golus and Birurim, not like a Tzadik’s relationship with Birurim. Page 89-90.

Therefore, Avrohom and Yitzchok quieted their opposition but they remained in their essence, while Yaakov corrected the essence and merited that all his children were Tzadikim. Page 90.

Yaakov couldn’t swear an oath whose entire end was to prevent confrontation that didn’t simultaneously transform the evil into good. Page 90-91.

Conclusion. Avrohom and Yitzchok could while Yaakov could not make a covenant with Avimelech. Page 91.