What's the point of wonderful eye candy if the thing works like crap? The reason old games keep getting played despite graphics that are poor by current standards is because they're enjoyable. Then modders come along and devote time and effort to making better pictures because that's something that doesn't require coding.
After all, 3rd party modders have made planes and weapons and ships and improvements to TK's stock terrains for years, all looking far better than TK could manage on his limited budget and schedule. But all those mods required the code base to be there to support them. That's what developers should concentrate on. I mean, look at Minecraft! Worst graphics EVER, since before Quake anyway, and it's a big hit because you can do stuff with it.
No one argues Call of Duty's latest doesn't look great, but the gameplay hasn't changed. If anything, it's more simplistic to play than CoD1 was all those years ago. Probably why people STILL play CoD1.