There are very legitimate reasons why we're seeing 10-speed automatic transmissions implemented in new cars, such as the Lexus LC500. More gears means a broader range of gear ratios without massive steps between those gear ratios. It means you can keep your car's engine closer to peak horsepower in order to achieve maximum acceleration, and it means you can put your engine in the right load and RPM range in order to maximize efficiency.
This video will dive into the details of why more gears can be a good thing, even with the negative consequences such as additional complexity, frequent gear shifts, and time lost in acceleration from more frequent shifts. The Lexus LC500 pairs a 5.0 naturally aspirated V8 to a 10-speed automatic transmission, and it sounds quick beautiful churning through the gears. That's not to say the transmission isn't without flaws. Check out the video for full thoughts on 10-speed transmissions and the implementation within the LC500.