I'd also point out it's not Reddit who wanted a $30 ARPU. It's a small number of Reddit execs and venture capitalists.
Reddit, by which I mean its vast user community, does not give a shit about ARPU as long as the site stays up and things get modestly better over time. And I've seen no evidence that Reddit needs a massive bump in revenue to meet those goals.
If they can’t make $30 ARPU stick, what could ever be profitable on Web, other than by deceptively recovering damages through ads? Is the only value prop of Web that it’s free-beer?(my mental answer is nothing and yes)
And they couldn't figure out how to transition to it without causing a shitstorm.