This is before me being old enough to follow technology, so below is a good portion of conjecture and hearsay (I'd love to be corrected by someone who actually remembers it):
Tim Berners-Lee initial web browser was intended as an editing tool as well as a viewer, and these ideas came back when they went to write up HTTP as a a "proper" IETF standard. Not uncommon (bit less so today, but back then especially) to design specs with what they thought it should do, not what they'd tried/done in practice. Making an official spec is the chance to get this stuff in.
At some point, a bunch of the file-specific stuff was split off to WebDAV as an extra thing (work on that started 1996, HTTP 1.1 was finished 1997) - or rejected and WebDAV created as a new home for those ideas? But PUT among some others survived.
This is before me being old enough to follow technology, so below is a good portion of conjecture and hearsay (I'd love to be corrected by someone who actually remembers it):
Tim Berners-Lee initial web browser was intended as an editing tool as well as a viewer, and these ideas came back when they went to write up HTTP as a a "proper" IETF standard. Not uncommon (bit less so today, but back then especially) to design specs with what they thought it should do, not what they'd tried/done in practice. Making an official spec is the chance to get this stuff in.
At some point, a bunch of the file-specific stuff was split off to WebDAV as an extra thing (work on that started 1996, HTTP 1.1 was finished 1997) - or rejected and WebDAV created as a new home for those ideas? But PUT among some others survived.