"The 5 mins it would take" --- Check the README on Red Alert, for example:

If you wish to rebuild the source code and tools successfully you will need to find or write new replacements (or remove the code using them entirely) for the following libraries;

    DirectX 5 SDK
    DirectX Media 5.1 SDK
    Greenleaf Communications Library (GCL)
    Human Machine Interface (HMI) “Sound Operating System” (SOS)

That still look like 5 minutes to you?

This is a terribly naive comment. I'm not going to even go into the specifics.

Lets assume they click one button and it recompiles, how many people would buy it? Almost certainly wouldn't pay back the dev and qa cost.

I am sure there are people who has moved to macOS that grew on playing eg. Red Alert 1 who gladly would pay some amount of money to instantly own and play it again for some nostalgia.

And by this I mean myself.

There are at least four dependencies that EA would have to replace for MAC. That would be an extremely complex task just for the first two. And who knows about the second. I just don't see a way for that to be profitable. Its no secret that games ported to Mac do poorly.

DirectX 5 SDK

DirectX Media 5.1 SDK

Greenleaf Communications Library (GCL)

Human Machine Interface (HMI) “Sound Operating System” (SOS)

Your assumed scenario was a magic button to recompile it.