I think they're presenting it as two separate problems. Drug infested is not describing the sex den. It is drug infested. It is a sex den.
Edit: Here's a good explanation: "A comma performs another kind of abbreviation in a headline, connecting two ideas without a linking word or phrase (often and)
Sooo back on reddit...
There is r/196. The rule of the sub is that if you visited it, you have to post a meme before you leave. These people are just following the rule.