That devices and services which offer old games sell well (see PSN, Virtua Console, Classic compilations and republishing of old games, HD-ports of favorite series, GoG and so on) to me means that not everyone wants to just play the most current games. Maybe you don't like to play old games, and that's totally fine. I also get the argument of an enthusiast with no time who says he'd rather play new state of the art-experiences instead of classics after 9 hours of work. Still, and I think I'm not alone, after 9 hours of work, I often prefer classics over new games since they are not as demanding to me (since I know them already and yet still like to replay them) and instead offer instant fun. To each his/her own.
I mean, you can argue that games - at least some of them - age badly. Then again, as others have stated, some games don't age at all or represent genres you seldom find today and in general stay relevant. Or maybe someone really would love to dwelve into nostalgia and replay FIFA 95 because he remembers how much fun he had with his buddys when they were teenagers or whatever. Like you maybe listen to old music or rebuy old movies for nostalgia - or for redescovering something you missed out on. I missed out on 16 Bit SEGA games (I was a Nintendo-Kid) and went on to build up a small collection of almost 20 classics over the last 7 years or so. I "only" had an NES and Gameboy and got an old Super Nintendo at around 2000 or so. Still buying games sometimes.
I find it sad that it seems so outlandish to think of games like movies in that regard. I speak for myself, but I watch movies from several decades ago up until black and white (can't really get into most silent movies, but black and white is a-ok with me. Watching classics from the 60s and 70s is especially rewarding to me personally, being a big fan of western movies, old scifi-flicks and the like). As stated, I also play games from several decades ago and still buy old stuff. I'd wish they were more easily playable on modern system. Now I get behind cartridge-based gaming not available on modern systems (even though... adaptors and stuff could be offered for a small profit, like the Gameboy-Player for the Gamecube, only that it plays N64 games or whatever), and I get technical difficulties and incompatibilities with programming to get everything to run (which often is only possible on much stronger devices if you don't include original hardware like the Playstation systems did, and it is expensive to program if you want a bullet-proof emulation)
Nevertheless, how uber-epic would a PS4 be when it could handle PS1, PS2, PS3 and PS4 games? That's probably not gonna happen, but entertain the thought - all of these are disc-based games. You could play ALL the games released from 1994 up to 2014 (that's 20 years of gaming!!!) on ONE system. Wouldn't this be of more value and also more convenient for you than to clutter your living room or wherever you play games with 4 devices (some of which are probably broken after extensive play, laser tech be damned) and a few dozen of cables and controllers?
I am sad that Wii U does not play Gamecube games anymore. Yes, I still have a gamecube. But as it stands, I don't really have the space for so many new devices under my television all at the same time anymore (my collection goes up until the NES, I'm sure I have more than ten gaming devices. Yet I'd like to be able to jump in and play classic games without keeping everything; and laser-based technology has the habit to break down after a few years of usage, especially in newer consoles it seems).
So in the end, you don't need it? Fine, to each their own. Yet calling it garbage is just wrong. (and actually.. when I think about it, why not offer several versions of, e.g., the PS4. Make the one that plays PS1-2-3 games 100 dollars more expensive for additional built-in hardware or emulators - I'd buy it. And when someone is sure they don't need it, they save 100 bucks. But yeah, I get that reselling old games on some download service is much more profitable for the companies involved ^^" I enjoy buying things I like twice! *sarcasm, kind of, I really enjoyed buying Jet Set Radio twice

*...)