If a manufacturer is trying to squeeze out as much HP, at the most cost effective way; a timing belt will win out every time.
I'm not saying its the best thing to ever happen in engine design; but it works well in so many ways.
The biggest thing to the manufacturer is the cost to produce a belt driven cam, rather then a chain driven. The next thing is weight 5-6 lbs of chain, compared to maybe a few ounces of a belt. Right there a belt is free HP; easier to spin something light.
The only downfall is the service intervals of a belt.