The reason some people do that is beyond my understanding.
It's not beyond understanding, though. Either they're lazy or they don't have the technical knowledge (or writing skills) to write their own whitepaper. And I'm sure many of you know that a lot of people around the world don't think anything of plagiarizing something from the internet, so since there are so many whitepapers that have already been written, in remittance.finance's eyes, why waste the additional time and effort writing something from scratch when basically what they want to get across to investors has already been written?
That's not to say it's right, though, and OP is to be commended for calling them out on this. Even if they're not a scam project (and I have no idea whether they are), this isn't a good way to start one. It's unfortunate that I've seen examples of this so many times that I've lost track.
Props, OP.