Why bidbot upvoting manually to just few countable users again and again . Even they have not good quality post

I visit some bid bots through steemblockexplorer. Then i realize that they manually upvote to just users not their quality posts. Almost their every post they upvote for curation.
I visit some of their posts that they upvoted only found few of them are quality post otherwise they are just images or little bit written.
That is not fair for the people who are making quality posts on steem . Steem bid bots should have upvote only one post per person per day.