There's a reason NES, SNES, Genesis, etc games are still celebrated: they can be found in person and lots of people have played them second hand. They've been passed down through families, to friends, sold and resold again. They've stayed relevant in the gaming community. Digital games and DLC will be a blip on the radar compared to physical games that can still be experienced 30 years from now. I say this as someone who's been gaming since 1987. I've researched where the industry used to be, experienced a great portion of what it's been through, see digital-only games cheapening gaming's cultural impact and value to society. Where will today's games be 30 years from now? Rotting on old hardware, assuming the mass-produced, poorly made parts even hold up that long. Gaming is being treated as if it is disposable, instead of an art form and a piece of culture.
I think you are romanticizing a piece of plastic, and your only experience seems to stem from consoles and that has left you severely biased. I have been gaming since 1987 too, but the platforms I started on were the Commodore 64 and ZX Spectrum and Atari 800XL and the Amiga, and my games ran off audio cassettes, and later on they ran off floppy disks, and later still they ran off the hard drive and the medium was never a part of the game, and later systems were backwards compatible so the platform wasn't part of the game either, and I say you are looking at the past from your perspective only and making connections where there are none. The best games have been ported and emulated and are still being played today even though the hardware is no longer around. Games that have had equally as large an impact as (S)NES games, that are played today even though not a single original medium or original box they ran on remains.
The reason games you speak of stayed relevant is because they were good games to begin with, not because the original hardware still works, and most of the people nowadays who play the old games play them on emulators and other machines. Everyone has played Pac-man or Tetris, not because they're bought/borrowed/inherited the original arcade machine, and not because the original hardware is still available, because "it can be found", but because it has been ported everywhere, and because it's fun. Games are not limited to their original hardware or the medium where they were once stored, and if people play them 20 years later it is because of the game, not because they happen to have the tangle of tubes and wiring it used to run on, or the plastic they were distributed on. If a game is bad, the mere fact you can pass it on won't save it from oblivion.
Online-only games get custom and pirate servers while the game is still officially supported, and there are ways of running them long afterwards, until a point in time where it gets a port, re-release or what have you and become supported again one way or the other. If a game fizzles out once support is gone, it wasn't that good of a game in the first place. If a game is good it will be played long after its original era/generation/platform has kicked the bucket
(and long after the "mass-produced, poorly made parts" - actually faster, more powerful and more efficient parts that inevitably come with the trade-off of being more sensitive; long after said parts rot away
), and 30 years from now games that deserve to be played will still be played, just like old games are (or aren't) played today. True, consoles are harder to crack, have patchy and inconsistent backward compatibility, and it takes longer for them to become emulated well enough to run games, and this is why to someone who plays only consoles it may seem that the only way to be able to play a game is to still own functioning original hardware, readable original storage media and working original online support, but for a large number of games, and a large number of gamers this is not true and never was.
A game's quality and draw has absolutely nothing to do with whether or not someone bothered to stamp out a few disks for someone who wants to caress and/or resell it. How does the fact a game is or isn't "digital-only" affect the gameplay, the design, the story, graphics, interactions, genre, any single part of the game? You don't use the data storage in any way when you play the game, it is no part of the experience. A game's quality has nothing to do with how it got onto your screen.
You may believe games are dropping in quality in recent years, they aren't as good or as fun or as impactful as the games of yesteryear, but even if this weren't just a case of nostalgia goggles, there are other, way more relevant reasons for it than digital distribution.
