It sounds like you need to read an entire article. The article argues that they're not incompetent but evil.

Essentially, plaintext allows them to email users their passwords periodically, which in turn allows them to increase user retention, security be damned.

I read the article. It's nothing but speculation and I don't buy it.

Emailing them their password gives higher retention than being sent to right location when you click on a link that automatically logs you in? Yeah, right.

Maybe that's how Markus justifies it to himself too but it doesn't make my original statement any less true.