I find it interesting that we don’t see more “officially-licensed demakes” of AAA games being released for devices (the Switch; phones; old PCs) that can’t play the AAA version. It used to be very common (with e.g. SNES games getting simultaneous GB reinterpretations released with them.) But the only thing I can think of that did it in recent memory is Final Fantasy 15.
But if you demake a game hard enough (i.e. really clamp down on the asset details, by using intentionally-stylized art rather than lower-quality realistic art, etc) then it doesn't need to take so much time and money to create the port. It can be a bounded added marginal cost.
Also, there are things a modern "parallel demake" (like FFXV Pocket Edition) can do to reuse certain types of assets from its AAA sibling, that in the previous era would have required remaking those assets from scratch. So a modern demake can actually be cheaper to produce in some ways.
For examples:
• You can just copy-and-paste the script and associated audio assets straight over, as anything can play audio clips.
• You can also copy over all the animation "choreography" scripting for NPCs and cinematics, with the particular named animation cues just mapping to different actual animations for the simplified models.
• Depending on how your AAA game models environments, you might even be able to export the abstract "level data" (what type of terrain goes where; basic geometry and material-type for meshes of buildings; placement of things like furniture and other large freestanding decor objects) from your AAA game engine, and then import it directly into your demake's game engine. (You'll then still need to run over everything to add new decor and details, make sure nothing is clipping, etc — but this is still a major speed-up.) IIRC this is how the recent third-party-implemented Pokemon titles [Let's Go Pikachu/Eevee and BD/SP] were implemented — they started with direct dumps and imports of the original games' level data into their engine.
Games used to take way less money and time to create, so it was viable to make 3-4 different versions of the same game for different platforms.