As part of the first Brood saga, Prof X thinks the X-Men are all dead but, through his depression (and unknowingly with the embryo of a Brood Queen inside him compelling him to recruit more mutants as hosts) he decides to start up another X-team. Still shook from losing the X-Men, Chuck demands that this new batch of younger mutants just be students learning how to control & use their powers instead of being a combat team. Therefore they can't be a "new X-Men," so they're just the new mutant recruits at a mutant academy ie "The New Mutants. Now the name is pretty lame but maybe that's the Brood's fault.
If you haven't read any of the New Mutants, I highly suggest you do. It's a large part of Claremont's classic X-Men run, crosses over with the main X-Men title a ton, deals with tons of heavy issues for what's supposed to be a younger X-team, great characters and characterization, Magneto becomes their headmaster for a really different dynamic for him and the team, etc... And the run where Bill Sienkiewicz does the art is considered one of the best runs in comics history
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fukking Fox and their writers man...
