There's a lot of copy-paste spam comments going on here on Steemit these days, and I think it all has to do with the fact that a some authors give them an upvote worth a few cents every once in a while.
They must think that they earn more about spamming hundreds of these types of comments without effort, compared to writing real and engaging comments. They are of course wrong - real comments obviously gives a better payout in the long term, and it is also a lot more fun for both the commenter and the author.