This question was asked in Quora and I have answered this question in Quora, shared in Twitter and additionally I am also submitting the same answer to this question as a backup in Steem blockchain.
The ecosystem of Steem is not designed to have a marketplace to use of bidbot to earn a positive RoI. The use of bidbot is still there but with a different purpose and that purpose is to promote the post only. So in order to save this ecosystem from exploitation, it is necessary that the bidder must pay some tax(get lower upvote than the bid value). Its purpose is not to make positive RoI and the Steem ecosystem was largely exploited with profitable RoI using bidbot for almost 2 years until HF21/22.
Normally what happens when a user buy profitable upvotes, the bot which receives SP delegation also earns a profit, which means the delegators also earn the profit. Then it becomes a cycle that encourages people to use bidbot to gain monetary advantage regardless of what the quality of your content is. That undo all the honest curation effort by other users and the content discovery is also discouraged.
HF21/22 (in Aug 2019) addressed this issue by introducing EIP(Economic Improvement Proposal). Now the community does not agree with the people who use bid-bots for profitable RoI and it must be taxing for the bidders so that their real goal of advertising their content remains intact. The users will focus on quality content only. The ecosystem will change into an ecosystem where there will be more content consumers, there will be more curation effort, ultimately the real goal of the proof-of-brain in Steem will be achieved.
Simply put, those who use bidbots for profitable RoI are downvoted by the community and those who use it for promotion(get an upvote lower than the bid amount) without profitable RoI are not downvoted(if it's not a low-quality content). That otherwise implies that the paradigm will shift to quality content only.
The users in the community are now empowered with full 2.5 free downvotes as a separate downvote pull is created(which does not deplete the voting mana). The users who use bidbots to buy upvotes with profitable RoI are downvoted. Further, if they promote a low-quality post they are also downvoted. So now the abusers can not afford to have negative RoI for poor quality content, which means they will do away from abusing the system. The bid bot who has a large amount of SP will be forced to curate more as the demand to use a bot will go down. So the ecosystem will further improve with more natural & organic curation effort from the bots. The other users particularly the middle-class community will follow the trail of organic curation management.
This is what #newsteem with EIP is and the content discovery, curation management are in a positive correction in Steem ecosystem(which was abused heavily until Aug 2019), the proof-of-brain got a new life post HF21/22. The ecosystem is fresh with positive energy and organic curation & engagement are quite visible now in this ecosystem.
Thank you.