They aren’t inherently bad, in fact, they are great in some specific ways (better fuel efficiency, smoother acceleration, reduced wear and tear on engine and so on. They work really well in tandem with hybrid cars and are great for small cars that primarily do daily commutes.
They are also a lot cheaper to put in new cars because they are relatively simple compared to a traditional automatic and turn something very expensive and hard to replace into something hypothetically cheap and easy to replace.
On the other hand- they aren’t very robust and do not hold up well in situations that produce high levels of mechanical stress - ie towing and aggressive driving.
Because they reduce production costs, and it’s tempting for manufacturers to use them inappropriately or put them in places where they aren’t easy to replace.
If I was buying a Corolla or equivalent I wouldn’t think twice about a CVT. But I wouldn’t want one in a truck, and putting CVTs in a hard to reach location and/or selling a bunch of cars with cvts to people with bad credit seems like a bad strategy.