For people tech savvy. Do they even have to do anything to these games? Can't you just kinda... release them for digital purchase? Or do that actually have to make like technical fixes etc
Most retro game collections these days tend to be running inside an emulator, similar to the ones you can download right now on your home computer. However, since those emulators usually are open source, usually with terms that make it difficult to use on consoles (see: Night Dive Studios trying (and failing) to license ScummVM for their upcoming Blade Runner point and click remaster), most companies develop their own. Once you have an emulator that you can definitively say runs the game through to completion with no issues, then you dump the ROM in the emulator, and sell it. Each release is different however. For example the Mario 3D All Stars collection is half emulation half native, with various texture, camera, and control improvements. The Mega Man Legacy Collection has rewind features, and the SNK Collection has a full lets play of each game, as a video file, that lets you jump into the game's state from any point in the video. Each of these features requires work to get going.
For something like the Wii's Virtual Console however, just selling a ROM bundled with an emulator gets the job done.
Plus, each of these emulated games must pass current Sony/Microsoft/Nintendo quality checks, in terms of bugs, online v offline performance, letting it run for days without problem, etc.