Have you tried riding a modern 1x10 or 2x10 gear setup on a modern bike? If not, then you should.
Newer rear mechs are a mixture of form and function, the straight cable entry eliminates the usual loop of cable going into the mech and also keeps it closer to the frame so it won't snag on any "Trail Furniture".
The clutch mechanism maintains tension on the chain when using a single chainring on the front, pretty essential if you ride on very rough trails to ensure the chain stays on the chainring.
The main thing is.... It all works, extremely well, New XT brakes for example are amongst the best out there.
The new stuff is an evolution of what went before. Personally I love the M900 xtr chainset, but by the time M952 came around I really didn't like the styling, but no doubt it works as well or better than the previous incarnation.
No doubt "fashion" plays a part in it, but that's always been the case, it's just that fashions have changed over time. The Zee mech I use looks like some kind of mini Transformer and I like it