As someone with a metre-high stack of vintage recievers in his closet, I think a significant part of the appeal is the feelie aspect. If you put the guts of a Marantz 22xx in a black plastic case with a modern RCA logo in it, it would languish for five years in the back of a Goodwill.

But the feelies are the hard part. An attractive bespoke case is expensive to build and ship. Some of the stuff (high-grade tuning capacitors) probably simply can't be had in quantity without opening a new production line.

I know there are a bunch of DIY kits that claim to be circuit-equivalent to popular vintage amplifier designs, and there's the Akitika range, but they're still not really a turnkey "it's your favourite vintage model, but with zero hours on it"