However, curiosity requires that I ask what/how/why does any of that affect mobile-first web deployment in away that it is not addressed when a large chunk of that mobile use is broken? If you program yourself into a dead end, back up and take another turn.
Oh, it is easier in a mobile native where you get the benefit of hoovering up personal data on all of your users? Gee, let's not expend effort to make something work universally, let's instead take the easy route and make money on the side too. The fact that losing this large share of users because of one type of content is not enough of a decision to go the other route shows just how much money there is in the hoovering of data.
Still putting the blame on Tumblr.