Hello @Akdx,
@zoneboy and @futuremind already answered the bid bot part, but I felt like I need to answer the 2nd part of your question better:
"Why does the platform allow bidbots".
Well, it has to do with what the platform is: a Decentralized Blockchain.
If we were on a centralized platform, there would be an administration running things, banning and allowing features left and right.
However, this is a decentralized platform (the Steem Blockchain) so there's no administration banning stuff.
Sure, witnesses with a consensus could do it if they wanted to, but even if they all wanted to it would be counter-intuitive since the attractiveness of the blockchain is decentralization, which means people here expect not to have their freedoms limited - like by bans and getting their actions to be prohibited.
Cheers