Explain like I am 5: What is wrong with CVT?

What's wrong with CVT? A) Some of them weren't built very strong, so they fail earlier than people are used to cars failing these days. 2) Even when they work like they're supposed to, some people find it weird that the engine speed and the car speed don't rise together. A CVT uses a V-shaped "belt" usually made of metal plates, that rides in a pair of pulleys that have a matching V shaped groove. And these pulleys each have two separate halves - the closer together you squeeze the halves, the further out from the center of the pulley that belt rides, so the "bigger" that pulley is, as far as the belt is concerned. And, the further apart you let the two halves go, the further down into the groove the belt can ride, which makes it a "smaller" pulley as far as the belt is concerned. It's basically a pulley this **\\--/** wide that can narrow down to this **\\ /** wide, where the belt is maybe shaped like **\\-/**. The good thing is, instead of a set number of gear ratios from "first gear" to "whatever number the highest gear is," it has a basically infinite number of choices between its minimum and maximum gear ratios. So, you can always keep the engine at its most efficient RPM for the speed you're going. The bad thing is, this all puts a lot of strain on the pulleys, and the belt, and the mechanism that moves each pulley's halves further apart / closer together. It's a lot of friction, and a lot of heat, and it's hard on the transmission fluid, and it's hard on the belt and the pulley surfaces. So, it's expensive to make one that's robust, and the parts need to be big and strong, but there's not room so you make them smaller. And it's expensive and difficult to heat-treat everything so it stays strong and doesn't wear fast. And in the case of the 4-cyl Nissans from 2012 to 2019 or so, the company that made THOSE transmissions didn't do such a great job. So, the parts wear out faster than anything comparable on other cars. Changing the fluid frequently helps. Also, because there's "one best RPM" for making power, flooring the car tends to have the engine rev up to its power peak and stay there while the transmission changes ratios to speed the car up, so it feels weird to drive, it's a little like driving a motorboat - the revs stay mostly the same, and the vehicle speeds up in a way that doesn't match the engine's sound. Some people find that weird and off-putting. Nissan V6 fwd cars (altima 3.5, Maxima) used a better CVT. Nissan RWD cars used a different transmission. Nissan 4-cyl cars from 2020 and later use a different CVT that's better. So, those all last longer than the millions of Sentras / Versas / 2.5 Altimas / Rogues / Kicks / Jukes out there with transmission problems.