Honest question: Beyond "that's not the way it always has been", what is the problem with tabs on top?.
For those of us whose browse with many tabs open at once and frequently switch between them, tabs on top means a *lot* more mouse movement to accomplish this, which equals more time. Wasted time.
It may not seem like much, but it is enough to be a noticeable delay, and adds up. Putting the tabs back where they belong solves this annoyance.
This may not be a factor depending on your own personal browsing habits.
Regardless of whether a mission expands or contracts, administrative overhead continues to grow at a steady rate.