Yeah, it was more alienating than the introduction of Cowboy Credits. 

I took a look at the original post and many of the accounts that said they were leaving actually haven't posted since that period.

LibertasBR

econ

~Econ Monthly Check-in: April

Undisciplined

The experiment was initially called Million Sat Madness. I'm sure plenty of posts were made about it.

Many stackers left during, and immediately, after the experiment. I don't think it's the explanation for the decline of ~econ commenting though, because that peaked several months later.