Why do Americans say "less than five people"? [duplicate]

I thought "people" is countable, so we should say "fewer than five people"?

Being in the US for many years, I rarely hear people saying "fewer than," even with countable nouns like "people."

I presume this usage is grammatically wrong, but idiomatic?

Some style guides presecribe "less" for uncountables and "fewer" for countables; however, historical precedent does not support this stricture, and in some contexts the countable "less" may even be preferred. One such context is when the word is applied to a number or quantity rather than to a group of countable things or amount of uncountable stuff. This is why in mathematics the symbol "<" is read "less than" rather than "fewer than", even when it's expressing a relation between natural numbers. In your example, the phrase "less than" is applied to "five", not to "people".

One way or another, this is a matter of style, not grammar, so "fewer than five people" would be equally correct.

'Fewer' is more syllables. People will always prefer a word with fewer syllables than one with more in spoken communication.