The Red Devils have struggled to replicate the success that saw them become Premier League giants under Sir Alex Ferguson, who guided the club to the last of their 20 top-flight titles in 2013.
Ferguson's successor Moyes was sacked after 10 months in charge while Van Gaal clinched the FA Cup in 2016 but was also dismissed by the club board not long after that success.
On Saturday, the Dutchman hit out at United over his sacking, accusing the club of putting his "head in a noose" before he was "publicly placed on the gallows."
Mourinho told The Sunday Times: "There was an evolution in the other clubs; there was no evolution in this club. In all the areas that make a team successful, I think we stopped in time.
"That was quite an empty period in the club with no evolution in areas that are important. It was the weight of the past on the shoulders of the players, managers, even boards, even probably owners, because when you are used to 'win and win and win', and suddenly you stop, it's like a heavy burden.
"Today, we have better working conditions, a better medical department, a better analysis department, a better scouting department, a better media department, and in many cases we did it without changing the people, which is quite important."
Mourinho won the EFL Cup and the Europa League in his first season at Old Trafford.