Part of the FDAs job is making sure the pill you swallow is the pill you think you are swallowing. It would be very bad if you thought you were taking penicillin and instead took sugar, or Prozac. This is a government task even a libertarian could love.
Sometimes enforcing a definition is harder than penicillin vs. Prozac. For example, condoms. The FDA has definition of a condom, and if your product doesn’t meet it, you can’t sell it, or at least you can’t call it a condom. Some of this is good. You want condoms tested for structural integrity, and you don’t want flat pieces of latex being sold as sexual health devices.
The FDAs definition of a condom does not appear to account for human variation. Condoms must be at least 160 mm in length. Condoms are not allowed to be wider than 54 mm (-> diameter of 170 mm). I’m not sure exactly how closely condom dimensions need to match penis dimensions, but that is longer than ~70% of penises and (using a condom width to girth conversion I don’t understand) narrow than ~18% of penises (source). Yes, condoms are stretchy and will fit over your leg if you try- but they’re more prone to break, and your leg isn’t kept rigid via blood flow. A too loose condom will just fall off, but a too long condom bunches, which also causes breaks and reduces blood flow.
I understand why we had to put up with this 100 years ago, but condoms used to be custom made, and some genuises in England are bringing that back. But thanks to our FDA and its scrupulous definition of condoms, it is illegal to sell them in the states. And it would definitely be illegal to use the cheap package forwarding service they link to, unless you are an EU citizen.