Romelu Lukaku made a transfer request at Chelsea before being granted a temporary move to Everton.
It is understood the 20-year-old Belgium striker asked to move following the European Super Cup shoot-out defeat to Bayern Munich in Prague at the end of August, when he missed the decisive penalty for Jose Mourinho's side.
Lukaku did not believe he could compete for a regular starting place for the lone striker's role after the arrival of Samuel Eto'o to join Fernando Torres and Demba Ba.
His request was immediately rejected and a loan with Everton negotiated on September 2, transfer deadline day, with his season-long switch ending the prospect of Ba leaving Stamford Bridge on loan.
He also impressed during a previous season-long loan deal with West Brom, during which he scored 17 goals - more than any Chelsea striker managed in the 2012/2013 campaign.
But when quizzed as to the thinking behind allowing him to leave again, Mourinho said: "Romelu likes to speak. He's a young boy. But the only thing that he didn't say is why he went to Everton on loan.
"My last contact with him was to tell him exactly that. 'Why do you never say why you are not here?'
"It's something that he should say, because he likes to speak, the reason why he is not with Chelsea and he is in Everton."
Mourinho believes there are a number of positives to Lukaku playing at Everton though.
Mourinho added: "It's good for his evolution. It's good for Chelsea, because he belongs to us for a long time and I'm happy with that.
"I'm happy that he's scoring goals against our direct rivals and he doesn't score against us because he can't.
"It's phenomenal when you have a player even when he's not playing for you he's scoring against your opponent. That's very, very good."
Mourinho stated he is unlikely to sign players this January - "most probably we are going to end with this group," he said - as few players are available who would improve his squad and be available for the Champions League.
Chelsea have won the title once since Mourinho's departure - with Carlo Ancelotti in 2009/10 - after he delivered the club's first championship for 50 years and successive titles at the start of his first spell.