What facts are there that they sold out? They added an optional 'show some ads' feature, only allowing those ads that followed a very strict and well-defined list of parameters. It's very much optional, and not hidden at all to turn it off.
From [1]. I'm not sure what better fits the definition of selling out.
[1] https://techcrunch.com/2013/07/06/google-and-others-reported...
> We receive some donations from our users, but our main source of revenue comes as part of the Acceptable Ads initiative. As detailed below, larger entities pay a licensing fee for the whitelisting services requested and provided to them.