This is a classic outside the field vs inside the field conceptual disagreement.
From the outside, the hard part of designing a chair is making a blueprint. At least making a blueprint looks hard to people who've never made one. According to outsiders, the next layer of the onion is perhaps inserting reasonable constraint dimensions for similar reasons.
From the inside, as a guy who's recreationally made furniture, the hard part is judgment about joint selection and design, experience with wood warping (all wood changes shape with the seasons, a good woodworker makes it look easy to work around and a bad one makes expensive firewood that rapidly falls apart). Another insider PoV is judgment about wood selection to get the correct balance of final finish durability and appearance. Finally working toward outer layers of the onion, its time to do parametric joint design decisions... What's the ideal number and size of dovetail joints for, perhaps, a drawer.
I've seen prints of chairs before I don't need a LLM to make one similar to the ones I've seen before and could probably make from memory (at least ones I built myself), the library has loanable books and woodworking magazines. I do see the attraction from the outside.
Consider something like a Windsor chair. The larger the wedge in the spindles the tighter and longer lasting the chair until you break something trying to force them in; there's a lot of judgment and experience in designing, selecting, and installing spindles, but none of it is written down so it'll be hard to train a LLM... Tighten it until it breaks then don't tighten it that much next time. Most super detailed plans for Windsors are for inferior machine produced replicas which are not necessarily useful for a fine woodworker and are not exactly what craftsmen would aspire to. People who want "a cheap chair" will buy a 4-pak of folding chairs from walmart anyway, not make a homemade Windsor-style chair.
Another somewhat more blunt example is for actual woodworkers the "problem" with hand cut dovetails isn't knowing what they look like or how to make a diagram of one, but gaining the experience behind a hammer and chisel to push your luck while cutting them as far as possible without going too far and turning the part into scrap. One unavoidable part of woodworking is I've turned quite a bit of wood into scrap on the last step; oh well make another. At least I can burn scrap wood to keep warm LOL.
Its kind of like from outside the programming fraternity the non-programmers think the only skills required to program are typing real fast and being very experienced at fizzbuzz during interviews. But that doesn't work IRL, from an inside-out perspective.....
The woodworking world is not exactly lacking for a library of "semi-decent" plans. An automated system to make enormous quantities of low quality unverified and untested plans would not really help the field, no.