They are called bona fide occupational qualifications. Even a private business can discriminate against say, an actor who can’t play a particular role due to the race or gender of the character. Same goes with certain jobs that involve lifting or an expected level physical fitness.

Many reasons that's not protected:

1. The "Genetic Information Nondiscrimination Act" specifically bans using "Genetic Information" in certain circumstances, which is generally understood to mean e.g. DNA testing. Discriminating on height does not fall into this.

2. You could still fall into issues with e.g. the Civil Rights Act of 1964 by having a height requirement if e.g. far more men than women fall into that height range, however there are exceptions[A] built into that act when a job has specific requirements, one being you can ask for "male models" to model clothing targeted at men.

A: https://en.wikipedia.org/wiki/Bona_fide_occupational_qualifi...

> Why are people outside of this range not protected?

Because legislation has been written to target certain characteristics. The experience of short people in American history doesn't quite match that of black, gay, or disabled people, and thus it hasn't been legislated.