Ultimately, I think GM books and premade adventures are failing the power-to-weight requirements of modern gaming. D&D is getting away with it because D&D sells itself these days with nostalgia. It's a remake of 3.5, not a modern OSR. There's also the matter that only one company on earth can really sell supplements in enough volume to be remotely worth it; WotC. Every other company or publisher out there is probably going to get edition sales in the same order of magnitude as D&D's supplement sales.
But the problem with supplements is that it's fundamentally designed for adventurers who aren't that experienced and aren't that genre-savvy, and for playstyles which aren't that open to lateral thinking because sometimes it works great, sometimes it could break the plot. Back in the late 90s and early 2000s, most of us were highschoolers. I don't know about you, but I had maybe 2-3 years experience with RPGs back in highschool, and I had consumed maybe about five dozen books or series relevant enough for me to brainstorm solutions with them. Today, I have about two decades of RPG experience and I've consumed about five times that much fictional content in other media. I've taken a university literature class on Sherlock Holmes, for instance (one of the few university classes I took which was worth the tuition).
I just don't approach roleplaying the same way I used to, and supplements don't really fit how I play the game. I'm not going to say I outgrew them, but I certainly outgrew the style of supplements I'm familiar with.