What you get is a physical reality. You can be reductive in describing the cartridge, just like you can describe a human as "mostly a bag of water", but it misses the point.
The old cartridge is a *thing*. An NFT isn't. It's more like owning the *receipt* of an old game cartridge.
Or even clearer, NFTs are quite literally exactly like Star Naming scams. You don't buy the star, the rights to it, the resources from it, or even the privilege of actually naming it in some official capacity. You simply buy a certificate saying "Wow, you named this star!"
You buy an NFT and you own zero rights to it. You don't have a physical original, you don't own the copyright, you can't reproduce it or have it printed on t-shirts. You just own the certificate and can resell that certificate.