Probably a difficult question to answer. My sense is that high quality new hardwood furniture hasn't gotten especially more expensive over recent time (adjusted for inflation) but you'd probably have to ask someone in the industry who is more plugged into various cost inputs.

>seems unrelated to (e.g.) sturdiness or expected lifespan

I'll disagree somewhat. At least in New England, there are smallish manufacturers who make high quality products that you're not going to find in most, if any, of the large retailers.