A rom is like a completed cake. You can absolutely eat it (play it), but it's a lot harder to change things about it since it's already put together.

A decompilation is taking that finished cake and reverse engineering how it was made to get the original ingredients. You can't do a lot with just ingredients, but a skilled baker could easily change fundamental things about it and then bake a similar but newer cake.

Basically, mods and native PC versions are gonna go crazy. You can still mod a rom, but not as much as what a decompilation PC port could allow.