Individual Youtube creators in the US most certainly are concerned about the FTC and about this rule specifically because they do not want to find themselves in court explaining to a judge why they shouldn't pay a big fine.

Also, if the creator doesn't follow the rule, the sponsor can be fined by the FTC, so even before the FTC notices the violation, the sponsor will probably notice and refuse to continue the relationship unless the creator's videos comes into compliance with the rule.

Again, this rule has been in effect for decades in the US. Advertisements in the US must be labeled as such. Ditto paid endorsements.