The Italian, who now coaches Russia, was in charge of England between 2008 and 2012 but they lost 4-1 to Germany in the second round of the 2010 World Cup.
And their long wait for a major tournament victory continued at Euro 2012, when they went out at the quarter-final stage under new boss Roy Hodgson.
Asked why England regularly fail to deliver at such events, Capello said: "Because they're tired.
"They're the least fresh of any of the competing national sides, because their league doesn't have a break.
"It's like when you're driving a car. If you stop halfway to put fuel in, then you'll definitely get where you want to go but, if you don't, then there's always the chance you'll be running on empty before you reach your goal.
"In my opinion, the football played in the first half of the English season is much better than in the second half.
"And, because of that, if you want to be a competitive team in the Premier League, you need a really big squad, which is a luxury you don't get with the national team."
'A good legacy'
Despite the 2010 disappointment, Capello thinks his time in charge of England was fairly successful.
"I think it went very well, but it could have gone even better," he said.
"The way we went out against Germany still hurts. That aside, I feel satisfied.
"I arrived after the team had missed out on qualifying for Euro 2008 but, under me, we easily made it through two qualifying campaigns.
"My win record was very good and I also gave loads of young players a chance, such as Danny Welbeck, Jack Wilshere, Phil Jones, Ashley Young, James Milner and Joe Hart.
"Theo Walcott had already played a game for England but he established himself under me. I feel I left a good legacy."
Asked if the England job had been more pressurised than his current post, he added: "On the pitch perhaps, yes, but away from football you can live very well in England.
"The English media put you under an awful lot of pressure, that's very clear, but it's hard to compare that with what happens in Russia, because here I can't understand what the journalists say!"