Minecraft wildly popular it's not about the graphics
I have defended the graphics using Minecraft as an example either on this board or on UO.com, and I have a kid in middle school and a kid in elementary, and Minecraft has, by far, been played more often over the last 4 years in my house than any other game and it's not even close. Our main Minecraft machine has an NVIDIA RTX card, which means Minecraft is not some outdated-looking 90s holdover, but a glorious ray-traced high-resolution beast of a game. We've seen the movie twice.
And I have even mentioned that UO's style of graphics are very popular for certain genres (particularly popular in Asia/Japan, but also here) and you can go on the iOS App Store and Steam and see a lot of examples of either pixel-style art, or the isometric views.
But at the end of the day, it is a problem, both in terms of feeling outdated for many potential players (or former players who bailed for other MMOs), and also in content creation (getting new stuff into the game) and the interface. I'm not going to rehash arguments I made 20+ years ago on the old UO.com forums, nor do I want to start the millionth round of the client wars. The graphics are what they are.
My kids were not drawn to UO for the graphics, they were drawn to UO because they knew I spent a lot of time playing it, that my wife had played it, that I had an entire shelf in a book case devoted to UO, the physical boxes (my son wants to keep my Charter Edition set), the maps, the books (some fantastic Japanese books that never made their way across the Pacific except through eBay), the figures, and various things (UO mouse pads, Origin stuff, etc.).
There's a lot of MMOs out there these days, all kinds of different art styles and perspectives. I don't need a full-3D MMO - I have that with Final Fantasy and WOW to an extent, but I know plenty of people who want something slightly more modern-looking, at least the interface has improved (the EC has come a long way and Pinco's is amazing when it works for us, and ClassicUO is great),. They would be intrigued by the Kingdom Reborn screenshots and models, etc.,