There’s no such thing as 64 meg EPROMs. The largest EPROMs manufactured were 32 megs. So any Neo cart that used 64 meg mask roms, and was a high meg game, required flash roms in order to make a bootleg. There is only so much room on the original SNK boards for roms. So if you were limited to using original SNK boards and EPROMs, then piggybacking is one of the few choices you have to get the job done. There’s just not much space inside a Neo cart to be using large daughterboards to double the rom space available. So piggybacking is one of the few solutions. There are some repro SNES carts of translated super famicom RPG’s that were high meg games, and piggybacking is done in those cases as well.