What a good read about promoted tab.

*..The more people that read, vote, and follow users who promote their content the more people will be willing to spend to promote content. The more people spend, then more Steem grows in value. In other words, simply visiting the promoted content page and reading promoted articles helps boost capital flowing into the platform...

OFC when you know your content doesn't worth to be on trending or such, you'll go for bots.