The AR-15 design is over 50 years old.
It is certainty a testament to its efficacy and the brilliance of Eugene Stoner's design that it has served so long and become the most popular modern sporting rifle in the USA.
That it is over 50 years old means some AR-15 models can now be purchased using a Curio and Relic FFL as the rifles are now over 50 years old and still in perfectly good working condition. You can bid and buy on this one and have it shipped right to you using your C&R FFL.
That gun banners want to prohibit ownership of over 50-year-old mature technology that is in very common use speaks volumes, and it's also why they'll fail.