This seems like a very ill-thought-out change. You didn't give advertisers more "targeted inventory." You moved the goalposts on what counts as "targeted," while simultaneously removing the option to target by subscribed subreddit.

It's fine to enable wider targeting, but the problem is you also removed the ability to target more specifically, which will drive away advertisers focused on conversion percentage.

My recommendation: enable both "general" (recently visited sub) and "specific" (subscribed to sub) targeting. When displaying an ad, pick the one that has the highest CTR for the current subreddit.