Tumblr infamously had a lot of spagetti code back in the day, with both new and old features breaking all the time. Last I checked (within the past 10 months), my tumblr accounts still shows -1 likes.

I think Automattic has been good for the site code quality-wise, but also very much believe it when I see it. Plus, what happens when porn federates over to someones Tumblr dashboard?