There is a reasonable legal argument that says it shouldn't be, unless you are compensated for the time (at least under anglo-american legal theory). As it is, courts will often dismiss "unreasonable" no-compete clauses, but you have to spend money on a lawsuit to get there. I'm not completely sure if the FTC is the right place for this ruling, but I'm not unhappy with it.

It appears to be a late 19th century phenomenon. https://scnoncompetelawyer.com/short-history-of-non-competes...

As some people have pointed out, the action will probably be moving to trade secret and NDAs protections.