I think most of it can be explained by your very first sentence. Gmail is 15 years old. It has massive institutional inertia and clout. Hundreds of engineers (h

I think most of it can be explained by your very first sentence. Gmail is 15 years old. It has massive institutional inertia and clout. Hundreds of engineers (https://www.quora.com/How-large-is-the-Gmail-team https://www.quora.com/How-large-is-the-Gmail-team), probably a similar number of PHBs. Some of those people have spent their entire professional lives working on Gmail. They are loath to admit it sucks. Understandably. You don't just phase that sort of thing out in favor of some upstart that came along three years ago. You can't. A category 5 shitstorm would ensue. Few people have the stomach for that. Fine you say, can't Inbox and Gmail at least co-exist? There again the answer is no. The usurper must eventually be vanquished. The situation is not long-term sustainable.