Short answer : because capitalism is a **transversal** marker and because most countries **take for granted** that they're capitalists. Why would you need to state that you're capitalistic when you feel like it's the default setting?
(so much so that they sometimes don't even realize that they are -- just like you when you write "the US are not so much of a capitalistic country", which is hilarious).

So they focus on **other aspects** of their ideology: for example, within the world that relies on markets, they feel like their differences come from something else, such as their type of government (republic versus monarchy versus whatever) or within the muslim world they focus on their religious families (are we more sunnites or more hiites or etc.)