When I was a kid, I tried really hard to create my own D&D stuff and it was always frustrating because it was never as good as I wanted it to be - it was hard to match the tone and style of Gary Gygax's writing, and even when I did so it always felt very derivative and inauthentic, even to me at the time.
By contrast, nowadays I can write D&D stuff pretty much effortlessly, and the results feel (at least to me) like they retain the spirit of Gary Gygax's stuff without just aping or copying it. I still don't think my stuff is as good as his, but I do think it's probably as good as or better than what most of the second-tier folks in the TSR design department produced, especially when you consider they had a team of developers, editors, graphics, and art people backing them up.
What's changed is, obviously, that I'm 30 years older now. I'm actually just about the same age Gary Gygax was when he was producing what I consider to be his best stuff (I'm the age now that Gary was in 1980). I've lived a lot more life and had a lot more experiences. I'm a lot wiser, and have a different perspective. I can see a lot more flaws and seams in the old TSR stuff that weren't apparent to me as a kid (and the more of the back-history I learn, through things like Jon Peterson's research and the El Raja Key Archive, the more obvious those flaws and seams become) so I'm not intimidated by them. D&D seemed totally magical to me as a kid. As an adult, I see through all the tricks.
And yet, I also still remember how that kid felt - how cool and strange and magical and slightly dangerous it all seemed. That memory - and the thought of how cool kid-me would have thought the stuff I struggled and wasn't able to write then but am able to write now without even trying is - and that's what motivates me to do it. This stuff doesn't really mean anything to me, but when I think about how much it would have meant to him, that makes it seem worthwhile.
This takes me back to one of the first posts I made here, about how much of the magic of D&D seemingly came from Gary Gygax playing with his sons - Ernie in the early years, Luke in the later years (and even Alex in the much later years). Even though I didn't play D&D with my parents (I tried once or twice, without success) and don't have any kids of my own (at least for now), I feel like that's probably the perfect representation of the game - parents and kids bonding through it. The kids get to feel grown-up and sophisticated by playing it, the parents get to remember and relive their own childish sense of wonder through the eyes of their kids. That dynamic feels much more special and magical to me than a bunch of nerdy college-age dudes in a game club, hunkered down in a basement when they should be out chasing girls.