Organisation A runs a traditional class that takes in 100 students. 50 complete it.
Organisation B runs a MOOC that, with a bit of advertising, gets 2500 people to sign up for free. 50 complete it.
Maybe my made-up numbers are off by orders of magnitude. But "2% completion rate" on its own doesn't sound so terrible if it reaches a much wider audience to start with - which both "free" and "online" could contribute to.
I have signed up to many MOOCs and completed a couple. I consider that a net benefit. MOOCs are not going to replace university education any time soon in my opinion, but for people who don't have the university option in the first place or want to take a single course every now and then they're a great thing.