@georgeob1,
I don't think that anyone really knows the motifs ... besides they themselves.
Johnson, Gove and Cameron have been buddies since Oxford university times.
I think that Johnson just wanted to become tthe new PM, without any plan what should or could happen after a Brexit - because he didn't believe it would happen.
Gove’s surprise move undermined Johnson’s chances of winning the internal party vote to be the new leader, but also seemed to make it unlikely that he could succeed either, given how many bitter accusations of betrayal it prompted from fellow and prominent Conservatives.