If they redistribute the rewards to people who upvote it then people like me (who never reads the posts) will upvote it just to get the steem back. That is definitely 100% vote buying as I am 100% vote selling for steem in return. The whole point of the curation rewards is to buy your attention and encourage people to vote for valuable content. Steemsports encourages you to vote for them. Twice. Four times a day. Every day. Regardless of whether you like the content or not.
Bottom line, I think @steemsports brings value to the platform, in spite of having a vote-buying component.
That's why I don't think they need to buy your vote.