They have, as far as I can tell. Last month I tried to set up a new 1PW installation and exhaustively searched through the app menus - no sign of standalone vault support anywhere.
It's possible that it was hidden because I had previously signed in to my work's 1PW account, maybe, or that it's hidden too well for me to find. I don't know, and would be happy to learn either way.
iirc (it has been a while since I used it), this fits with what I saw. You could do it if you set it up as a local vault at the very beginning, and add a web account on top of it, but if you started with a web account it was not an option at all.
It's possible that it was hidden because I had previously signed in to my work's 1PW account, maybe, or that it's hidden too well for me to find. I don't know, and would be happy to learn either way.