Like a lot of changes to modern vehicles, the change is driven by fuel economy requirements.
In years gone by, had a lot of 4 speed sticks. Then it was 4 with electric overdrive, then a true 5. My first 6 speed was a 2013 Jetta TDI. I expected it to be a gimmick. It was not. Mileage was better than my much lighter 5 speed Jetta.
My Jaguar diesel has an 8 speed auto, and it uses all 8 gears. Out on the open road the engine is always running at a speed that gives optimum economy or performance as requested by the driver. It is quieter and faster than the Jetta, and gets better fuel economy. And, it appears that they did not cheat to get it approved.
As for other vehicles, I have driven a 3 axle water tender with a 10 speed manual transmission. It needed it to keep the engine spinning at the optimal speed for efficiency. Actually, to keep the engine spinning at a speed that would move the beast when it was hauling 3000 or more gallons of water.
All of my current mountain bikes use 1X gears. Either 1X10 or 1X11. The outer limit right now seems to be 1X12. My new road bike has 2X11, which replaced an older 2X9 bike.
Is it a gimmick? Not really. My average pedaling rate stays up around 90 on the new bike, which means I am always spinning at my preferred speed. That allows me to ride more comfortably and faster. Very much a win/win.
For all of these, cars, trucks, and bicycles, the only downside is cost. The benefit is increased performance.