The most common form of enforcement of any law, rule, regulation, standard or ethos is self-regulation. When the individual decides to comply on their own. If YOU decide to comply that day then the mere existence of the standard to which you can claim adherence will have served one of its purposes.
When you do comply, why do you do it? Because you're afraid of getting caught the moment you step out of line or because you choose to consider yourself in compliance, at standard, in sync with your responsibilities, or whatever other reasons. Because you want to be in, not out. You don't comply out of fear of being punished by the govt, or if you do then that's not the main reason.
Enforcement isn't part of TAFs job description. It's on the lenders to accept or not accept, on their regulators to enforce lending regs, and on the state regulators for the appraiser licensees. And of course on the individual appraiser to decide that today they're going to be a professional and not a donkey.
Without a standard there is literally nothing for anyone to enforce in any manner. There's no defensible position for the appraiser to claim they're in compliance, there's no basis upon which to disagree with a peer or a reviewer or an underwriter. Etc. But by the same token the mere existence of appraisal standards isn't a guarantee of performance, just like holding a license or an appraisal designation isn't a guarantee of performance.
Just because drivers commonly speed doesn't mean the speeding laws aren't effective and shouldn't exist.