I would guess too a better investment in colonies. The US spent its time and effort effectively colonizing the rest of the US. And grabbing a few islands to be fair, but those to my knowledge have been mostly good investments still. Importantly, the US also integrated its colony efforts. The US is considered one, inseparable country. Compare that to a map of the British colonies pre-WW1. Sure, they had enough territory under their control such that the sun never set on the empire, but it overall didn't do much for the country. Then with the stresses of WW1, they lost most of these colonies, as they never were really integrated into the country.