Apparently, the reason why some kernels don't pop is because they have too little moisture due to the hull not being perfect and the moisture escaping[1][2]. So it seems like it should be possible to somehow go through all the kernels and remove most of the unpoppable ones? Maybe make something that weighs each kernel and removes ones outside a range?

1: https://americasfavoritepopcorn.com/blogs/all-blogs/why-do-s... 2: https://popcornity.com/why-some-popcorn-kernels-dont-pop/