In the months before his departure Moyes repeatedly spoke about the need to rebuild the squad he inherited from Ferguson.
But Robson told Sky Sports News: "It was for personal reasons - not professional reasons - that Sir Alex got out.
"I still say that you look at the squad and it was pretty good: they won the league by 11 points; the year before that they only got beat on goal difference by Manchester City on the last day of the season.
"These lads have been in there, they've seen it and done it, and there's quite a few of them that are still young. Yes, we've got Rio Ferdinand and Ryan Giggs getting on a bit, but the other lads are at the peak of their career.
"I can remember people saying I should pack in at 34, and when I was 35 or 36 I won two championships with the club.
And Robson reckons the Glazer family were right to act if they did not trust Moyes to spend the club's money wisely in the close season.
He said: "I believe when you're an owner or director of a club you've got to make strong decisions.
"If you have got that amount of money to buy players, you've got to be 100% sure that the people who are going to spend that money are doing it in the correct manner.
"If you don't make the right decisions with that money that's when clubs get in big trouble. Whether that would have been the case with David we'll never know because the club have made the decision."
That decision leaves Giggs in temporary charge, and Robson said: "I definitely think he's going to be a manager, but whether he gets it full-time at a club like Manchester United is a big ask."
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