UI UX Designers

What do they do exactly? Many of them are earning well. I'm referring to those who work in big MNCs or large startups. I can see many companies with little to no ui changes over the years. And there are some companies which don't require a ui designer to work everyday as their products are deployed and there are less changes over the years. This made me question what the hell they are doing. Some even start with 50+lpa with no experience, in tech companies. I would also like to mention that some of these companies which hire designers for big bucks don't even have a good ui. Are companies giving away money for them to do nothing? These are based on some people I know who work in this industry.