Lack of testing is part of it, most places do less testing than is ideal. But there’s much more to it than that. From the article, the author’s resolution is 1

Lack of testing is part of it, most places do less testing than is ideal. But there’s much more to it than that. From the article, the author’s resolution is 1366×768. This was designed and tested for! The problem wasn’t that it was broken at that res, the problem was that it was incorrectly classified as a tablet-only resolution. The issue here is their designers and developers being out of touch with their users, and using constrained hardware helps with that.