Keane joined Everton for an initial £25million after an impressive season at Burnley in the Premier League.
The 24-year-old had been an academy graduate at United but was unable to break into the team and left them in 2015.
But when presented with the opportunity to rejoin his boyhood club, Keane opted to play for the Toffees and the guarantee of regular football.
And Keane admits his decision was made for footballing reasons.
He told The Times: “They [United] were in touch with my agent and showed a lot of interest.
“They wanted me, but a few things happened and I thought Everton would be the best place for me to come.
“I thought I would get a lot of game time here, more than I possibly would at Manchester United, and that was a massive factor in my decision.
“My family are all Man United fans so it was not an easy decision.
“My dad would have been delighted if I had signed for United.
“But he is glad I have come to Everton and not Liverpool, put it that way.”