Why do Americans use the word “classmate” in school, but not “mate” when referring to actual close friends?

I don’t think there’s a “why.” That’s just the way we say it.

Also roommate, housemate, officemate, bedmate…but when we say “mate” by itself, it usually means a spouse or committed partner. We have lots of other words for “friend.”

Because.

I’m in agreement with @Jeruba

We have the maritime usage, animal pairs, chess. The term just never took over here as a substitue for friend, buddy, pal, etc. The Canadians too appear immune to the habit, and the Jamaicans as well. What about the Irish and Scots? We know the Aussies & Kiwis have succumbed. I’ve seen enough Paul Hogan movies.

I think it has something to do with the Southern Baptist religious influence and the resultant negative connotations of the term “mate” when use to refer to one of the same sex as yourself.

When modified i.e, roommate, people share a commonality.

When not modified, in U.S.parlance, the commonality is being paired with each other.

(Incidentally, “checkmate” derives from the Persian sha manad, the king is helpless.)

Mating habits involve sex. Americans think about that before ‘mate’ meaning pairs,

Although we use the word “playmate” for two friends in early childhood. How suggestive

^^True. If I hear mate on its own I think sex.

They like to feel special.

We Americans don’t think the British use of the word ‘Mate’ as sexual, however. Its just close to mating season, mating rituals, etc for our own use. It would be a little strange and we would fear misinterpretation among other Americans.

Well, that’s what we learned. That’s all.

I don’t automatically think of sex when I hear the word “mate.” Like, “He’s my mate!” I hear as “He’s my friend.”

When I see ;coffee mate’ coffee creamer I wonder how THEY would do it.