I never understood why that rule doesn't include comments. Like if you posted a ton of helpful comments and zero posts, you wouldn't be allowed to post a link you made yourself.

I don't think there's anything wrong with promoting blog posts or apps you've made yourself unless it's really excessive. How are people supposed to get started otherwise? It's okay if you're a huge tech site, a big newspaper etc. because people will auto-post your new posts to try to earn some karma but who is going to do that when you've only got a handful of readers?

That's not a rule, its a guideline from a page that states its "no longer updated".

Selectively enforced. I have a small enough profile and don’t advertise much and my account is nothing but promotions.

De facto the only enforcers of this rule are moderators, who care more about their subreddit-specific rules anyway.

The rule only Applies to small businesses.

Big companies buy accounts that have been used for years.

Accounts are pretty cheap to buy