Because the curation-algorithm, with its difference-of-square-roots function, gives higher curation weights to very early upvotes and larger upvotes. This leads to an early scramble by algorithmic-voters to get the best curation-rewards. The window superimposed a negative linear curve so that voting after a few seconds meant losing much of what could have been gained from the curation-curve alone.
The two algos then created an interesting complexity within the first 15 minutes (previously 30 min) that will now be squeezed into 60 seconds. Thus the faster bots can still play the same game and the maximal rewards will probably be somewhere within 60 seconds. This is like the history of high frequency trading in futures. We shall see how it pans out.
How about 1 identified human, 1 account, no automatic algorithms? Human must do a captcha-like Turing test for each upvote, post, resteem, etc. I suspect this would bring Steem in line with what most users think it is/should be.