I strongly believe "if you're already famous" part is the most disgusting part of self-promotion policies (in general, not with these examples), because popular creators get at least 10+ people that will post their content as a link for karma, and then people starting out get none of that benefit, and starting out is the most difficult phase.

If everything/everyone adopted a no-self-promotion policy no product could get any popularity. I think the rule is often instated for reasons really involving low-quality content and spam (but with more exterior objectivity), but it hurts the already-disadvantaged in the process. The only good thing that may come from it is having to focus on features and benefits of the product more since you can't just dump the link to the product, but again already-famous people/companies don't have to deal with that.