To be fair, that's not a true statement.
It's fine as an opinion (and more power to you: by all means advocate for the Realms you want to see published), it's just that the Realms has never, ever, been a setting designed solely for people who don't want to make things up.
Besides, it's impossible to run a Realms game and not have to make things up.
What makes the Realms "what it is" in the minds of thousands of gamers are the experiences they have playing D&D in the Realms, and that comes in large part from the words and deeds of their DMs and their fellow players, not from what's written in a sourcebook.
Just so we're clear: I'm not presenting and either/or here. For some it's the rich history, for others the loads of detail, for some it's the crunchy rules designed around Realms concepts, for most of the gamers I know it's reading a novel and then wanting to experience elements of that story at the gaming table, for many a DM it's the name and simple description of a place that set them off filling in the details, and for others it's just that the Realms happened to be the setting where their DM set his or her latest awesome game, and for most it's a little of all of these.
There is plenty of room in the 5E Realms for differing styles of play. If WotC wants to avoid the problems of the past, they need to build a Realms that caters to differing interest levels in the Realms, and make sure they present the place as not needing a Master's Degree in Realmslore before you can start a game there.
This is why I like what WotC is doing by setting adventures in the Realms first, sans any world sourcebook, so gamers coming back to D&D and new gamers just starting out can form the viewpoint that all you need to play in the Realms is an adventure and the Core Rulebooks.
Good job WotC. Keep it up.