The 19-year-old moved to Liverpool from the Hoops in February 2010, after the trio of London clubs were put off by his troubled life at home.
Sterling chose to move to Merseyside for a clean break away from the estate in Wembley where he grew up.
"Arsenal, Chelsea, Spurs, they all knew about Raheem. But their attitude was: 'Too small, too much baggage'," Gallen told London 24.
"At the time, I wanted him to stay at QPR. I persuaded the reserves to give him his debut at 15 so he'd feel he was being fast-tracked. But at one meeting, after training, Raheem said 'Steve, I have to go'.
"I could see how genuinely upset he was and I thought, 'I can't do that to a kid', so we reluctantly agreed to listen to offers. Now, with hindsight, I can see it was the right thing for him to leave, as much for a change in environment off the pitch."
Sterling returned to his former club on Sunday as Liverpool beat QPR 3-2.