The Atari 2600 homebrewers release the roms for their games all the time when they go out of print.
And there are at least a thousand times more NES collectors than 2600 collectors, and I bet you that 90% of them can be duped into buying a bootleg cart release of a limited edition game because they don't know better. 2600 collectors, on the other hand, do know better since they're much more niche and a tighter community.
Not to mention it's much cheaper to make NES bootlegs than 2600 bootlegs. Anyone can take a game and slap it on a new, mass-produced NES board. Or if they're hacks, a quick ROM swap and boom, new game for sale. I hate repro hacks and stuff but even I think that these limited edition carts are fine because they don't get pirated to hell and back.
If these guys really wanted to have their games played by everyone then they'd release the roms, true, but they don't, very likely for the reasons I mentioned - and that's their choice.
If the folks making the money on selling the cart for 4X the original price were the original developer I would agree with you.
But my point is the original dev wrote it. Designed the board. Manufactured the cart. Sold it for $50. Then they were done with it.
Some fortunate folks picked it up for $50. Some hoarders bought up a dozen of them and waited for it to go out of print. Occasionally some of those folks sell them for jacked up prices on the internets.
The devs are not receiving any benefit whatsoever from the inflated sales. So money clearly cannot be their motivation in not releasing the roms.
I understand the thinking of those that own a $50 cart that's now worth $200. But it is a double standard they are upholding and the thinking that existence of the roms depreciates the value of the physical carts is provably flat out wrong.
Roms are out there for Crono Trigger, Star Fox 2, Ducktales 2, and Bonk, yet those games still go for $100 or more! In some cases because they are rare. In other cases simply because people are willing to pay those prices.
Release the rom for SMB2j and people will still be willing to pay over $100 for the physical cart.
Thinking it through. I think I know the answer in the case of the Retrozone stuff.
The only thing I can think of is the devs are either afraid of legal action since the repros I mentioned above use graphics and IP from Nintendo. and/or they plan on doing a reprint at some point (unlikely since they use graphics and IP from Nintendo).