How many people born in CH never become Swiss? Because for the US, that number is ~0%.
And before you say: "well the US have different rules", well, ok, but then don't compare us to the US on the other number either, compare us to other EU countries with similar types of rules but different implementations.
CH has stricter naturalization laws than many EU countries and CH has mandatory military service which discourages many males from naturalizing, even those born in the country.
About one third. That would bring the fraction of naturalised foreign-born citizens in line with the US (which is also a kind-of-hard place to get citizenship, that's true).
> CH has mandatory military service which discourages many males from naturalizing
That doesn't make it difficult, it makes it undesirable and suggests that many people could get it but choose not to.