People have different tastes. Just because something is old or handmade, that doesn't make it desirable.
Plus, 140 year old furniture takes specialized maintenance if you want them to last. It's kind of expensive to properly maintain or refinish antique furniture. Chairs, especially, need proper maintenance, they experience much more wear than something like a chest, and an improper fix can destroy it.
Older furniture can be much easier to repair its just a shame that the knowledge is somewhat less commanplace than it once was. Shellac finishes are a known quantity, easy to touch up or remove an re-apply. The animal glues used in woodwork of the past also allows joints to be easily disassembled for repair and often you can just reactivate the existing glue with some moisture and heat.
Of you break a spindle or a stretcher, especially at a tendon, then doing a proper fix does take skill and specialized tools. Disassembly really isn't an issue, because, like you said, some heat and pressure will release most joints with ease.
But actually fixing a break does take skill. If you're lucky the pieces will mate back together seamlessly and you can use wood glue and maybe some wax to get the piece looking like new and just reassemble them. But if the break is not clean, or there has been a previous repair (maybe involving screws or nails) then replicating a piece is pretty difficult. Turning a new piece requires a lathe, color matching stains is definitely a skill you acquire through experience.
Chips on surfaces and the like pretty much require you to have a decent collection of veneer on hand, in order to luck out and find something with similar grain patterns.
I do a fair bit of antiquing and (proper) refurbishing of old furniture (not 'upcycling'). It's not for the faint of heart. It's a time-consuming labor of love that's akin to maintaining a classic car.
Plus, 140 year old furniture takes specialized maintenance if you want them to last. It's kind of expensive to properly maintain or refinish antique furniture. Chairs, especially, need proper maintenance, they experience much more wear than something like a chest, and an improper fix can destroy it.