It doesn't help that original GB cartridges backed the data up by having old round CR20** series to power a memory chip. When the battery dies with no way of replacing them theres no memory chip anymore.This happened in some but not all GBA games too.
I lost several memory cards to old age. In fact it's why I need to get EPSXE installed on my laptop because I couldn't even if I had my ps1 set up play my games because otherwise I'd be unable to save them.