It just gets renewed, reused, and recycled, not only in more wealthy Western countries, and Third World countries, but by poorer people all over the world. (Hopefully with Linux and other FLOSS software installed!) There was an article in Slashdot in 2013 about an IBM 402 with punch cards, still in use!!! (I wonder if it could run Linux?) ;^)
But seriously, even though most of us are using computer less than 5 years old, a lot of old computers are still in use. What about 16 bit embedded systems, many running Linux! I have to agree with Linus, if the old technology in the kernel, does not adversely affect newer technologies, and people are still using it, then there is a legitimate reason for leaving it in the kernel. I trust his opinion.
IMHO, I think the FLOSS community has an obligation to continue to support older hardware & technologies that certain other proprietary O/S manufactures have long ago abandoned. Isn't that one of the reasons the Free Software and Open Source Software communities, and software were created in the first place?