I agree with you post. I didn’t know about this feature request and I want to add my vote that it’s important. I’d created a topic post before seeing your post:
FWIW I think from a behaviour point of view, the earlier posts get deleted and the content merged into the latest selected one - which wouldn’t be possible with an OP into a second post. Though I’m not sure if there’s also a technical limitation/reason as to why it’s done in that way.
I would also appreciate this feature. It happens quite often that new users want to post more than one image. Because the nasty system only allows them to post one, they post the other images in consecutive replies. I know: if users behaved better, this wouldn’t be necessary… Being able to merge those posts without copying all replies into the first post and deleting them would make this less annoying.