Alderweireld ended two years of stalemate on Friday when he finally signed a deal that keeps him at the club until 2023.
Mourinho said, "Player happy, club happy and now in football, in this moment now, there are some people that it looks like they are more important sometimes than players and then the clubs, and these people they are very important sometimes in decisions, in solutions.
"And in this case the family and the agents were happy to make the player happy.
"So it was easy."
Mourinho is widely credited with getting Alderweireld's deal over the line as he made it clear from his arrival that the Belgian was a player he wanted.
"The club's objectives are exactly the same objectives as mine," he said. "To be more objective in this moment we are the club. I am the club.
"We want Toby, Toby wants us, the people that works with him were happy to make happen what the player wants, so it was not difficult.
"The statement for me was the beautiful, simple: 'I couldn't be happier in another place'. So if he couldn't be happier in another place, be happy."