Magic items served as a way to mechanically differentiate your character in early editions of the game, when one 5th level fighter was much the same as another. Dragon magazine would publish multiple articles decrying "Monty Haul" DMs that handed out magic items like candy corn on Halloween. Yet every NPC in the published modules and campaign settings was bristling with the things.
The "game balance"-focused design 3rd edition made things even worse by hardwiring magic items into its expectations for characters of a certain level, so that if for some reason you didn't have the "expected" items by the time you hit a certain level, you were going to get creamed by the encounters that had been designed for you.
I like 4th edition plenty, but where it really dropped the ball was on magic items. Early previews and hype coming out of Wizards of the Coast promised that the days of carrying around six different magic swords were over, but really, all the game did was make it more obvious how many points of bonuses you were supposed to have by the time you hit a certain level. Also, the game made it even easier for characters to create their own magic items. This is sort of good, because it means that you're no longer just hoping the DM gives you the "right" items - you can just make them yourself. This is also sort of dumb, because the real solution would have been to just make the characters competent enough that they wouldn't need piles of magic items.
I currently play a wizard in a weekly 4th edition game, and I guess it's neat that our characters can pretty much get whatever they need when we need it, but it seems really flavorless and boring to just say "my wizard spends 3000 gp and makes a sword +2" or whatever. I understand that the 4th edition designers were just trying to make it easier for players and DMs to do what they had already been doing for years, but really, I think the "D&D adventurers are magic item Christmas trees" trope is one that should have ended up in the junk heap along with "fire and forget" spellcasting. I can get behind the idea of a character with a magic sword, or magic boots, or a magic shield. I'm less interested in a character that has all three.