Not sure I know what you're talking about. Several artists I know promote each others comics however most of the time they do so willingly and unasked (just because they love the series)
Also on twitter, SO MANY awesome loving creator RT other creator's update posts, WIP sketches, and promotional artwork.
I'm sorry to read you've had a tough go at it but perhaps your approach is off?
Maybe focus on joining a community and forming bonds with other creators before asking for "shoutout exchanges". I find that shoutouts are more genuine when both are familiar with each others work.