Because USA was a superpower that can afford it easily. Taking the leadership in everything is quite cheap price to pay when the other end of the bargain is everyone else has to follow you.
Now of course USA is ceasing (voluntarily, by stripping down every international soft power effector in government) to be a superpower, to the great glee of dictators all around the world.
The "we can't afford being great" is a direct admission that USA is no longer a superpower. And is not going to become great again, just another nation again (at whims of China).
The nazis don't think that though, uh I mean conservatives. After they've burned down everything, they expect still to be a superpower somehow. Do they think they can just start a war with everyone who doesn't play ball? It's hard to comprehend what their rational is, if there is one.
Now of course USA is ceasing (voluntarily, by stripping down every international soft power effector in government) to be a superpower, to the great glee of dictators all around the world.
The "we can't afford being great" is a direct admission that USA is no longer a superpower. And is not going to become great again, just another nation again (at whims of China).