Such users mostly come from account farms, and they are don't care about their posts (contents, quality), or too lazy to spend a couple of minutes to read previous OPs, and previous posts, to brainstorm ideas, and to compose their on-topic posts; or they don't have enough time to do all those steps because they have hundreds accounts need to publish shit posts every day.
Either how good the poster becomes over the time, their primary intention would have been to spam, plagiarise and to get a higher rank certainly joining signature campaigns. If they would have come here for the sole purpose of contributing something they would have never copied other user's post.
Yes, it's different at somewhat extent, but there are common reason of plagiarsim. That is to steal words or ideas of others in order to get financial benefits. For whatever, signature campaigns, bounties (plagiarise to hit post quota); or to steal others words (such as Whitepaper, OPs, etc.) to lauch scam projects (for example).
Copying from a news article without properly mentioning the source is completely different than copying a forum member's post. Jace Lee have used text spinning and tried to make the post as his own post which isn't really appreciated. I don't report newbies who forget to add a link to their post if they have shared a news article since in the beginning most of us wouldn't be really aware of posting a link.
