That's because that's not a contract. Real contracts can only bind people who sign them, but in places that don't recognize right to work, you can be forced to join a union just because 51% of your co-workers signed.
"Right to work" only covers whether you can be made to pay union dues as part of this arrangement.
Contracts deprive non-signers of things all the time. That's kind of the point.
Do you have a problem with corporations signing "exclusive" deals with other corporations?
This is absurd.
You’re saying a corporation cannot enter into a contract to be the exclusive supplier of a widget to another corporation?
“You can’t hire anyone else willing to work for less than $x” is extortionate. Competition is necessary for a market.