[auxbuss]

Why are authors allowing this?

Whenever I've been published, I've asked to retain copyright and that has been granted -- I'm not sure it's a grant, though, since it's mine to start with. The usual negotiating starting point is a contact from a publisher that automatically claims copyright. I simply delete that clause (and possibly insert "The author retains copyright", so that there's no doubt).

Clearly, that's not happening here and I don't understand why, unless publishers are refusing to publish without being given copyright. In which case, alarm bells should be ringing very loudly.

[coriny]

It's not about handing over copyright but it's generally agreed that publishing multiple copies of the same work is a bad thing. This is typically done by researchers to boost their paper count (+ a bit of self-citation), and can make a hypothesis seem better supported than it is.

So only dodgy journals will re-publish work that has been published elsewhere.