This isn’t aimed at you specifically, but there seems to be a misconception on how simple and straightforward it is to “update graphics” or do X game in a newer game engine. Upscaling textures, re-working animations, adding particle effects, shadows, cloth simulation, all take significant effort on the part of artists and engineers. With these older games that are just on life support with a skeleton crew, it’s not obvious that making a game look prettier to attract new players will yield more revenue than pumping out new content and retaining established, loyal players. With a small dev team, you simply can’t do both.
As far as porting an established game to a new engine goes, unless your game was built in a legacy engine (like Unreal or Unity), you can’t simply push a button to update your game (and even in those engines there’s unforeseeable incompatibilities and bugs that will result from the update). For example, when Tyen shows his prototypes for EQ in a browser in Unity, he’s manually transferring art assets from EQ into Unity. They’re just the assets though. You have to manually establish collision, interactions, etc. All gameplay (mechanics such as agro, skills, targeting, etc) also requires someone to code (or script) by hand. There’s no way to upload the rules and code from EQs engine into Unity.
Granted, there’s a lot of potential for us to use machine learning and have AI play legacy games and port them into newer engines. I haven’t seen anyone talking about this, but I have to believe it’s being looked into if not already being attempted. However, with the tools currently available to us, transitioning games into new engines is a matter of literally recreating an old game, line by line from scratch, in a new engine. There’s nothing simple about it.