Yes, incompetence. I bet that such a defense would have trouble in court considering that your resume and interview would ideally cover the true amount of years of experience.

"Never attribute to malice that which is adequately explained by stupidity"

It's not malice, it's business and legal acumen.

If that's what the legal department recommended to me as a business owner to add in protections for being able to fire employees, I would fire the legal department.

How many applicants will be inspired to lie because of my absurd requirement on the job spec? Of those applicants, how many will I hire? Do I only hire applicants who have lied in order to be protected so I can later fire them? I wouldn't hire someone who lied on their application in the first place!

I've never had a legal department recommend something so silly as this, and I challenge you to find one that does. If you want certain protections for the company in an employment agreement, you put them in a contract.

"never say never"

Bieber's Razor?

They're either looking for a purple squirrel (like trying to hire the original developer of the technology), trying to move someone internally into a position that requires them to also seek outside candidates (by making the requirements impossible to fulfill), or dev told HR they needed someone with "X" experience for a senior role, and HR translated that to "10 years experience with X" (X having been out for 2 years).

There are three of the standard answers that come up any time this topic does.

I would say the next step here is to look at who actually gets hired, but I have no way of accessing that.

If we're going for impossible, then it sounds more like the old H1-B 'we couldn't find any qualified applicants' trick.