Thumbnails are fine, and so is capitalization in titles (e.g. if your video is news about NATO, you probably want to write NATO in all caps in the title). The only problem is misleading and/or intentionally vague thumbnails and titles, and the much bigger problem is that so few people care enough to never click on clickbait that almost all creators have to do it if they want their videos to succeed even if they dislike the practice, which makes it very difficult to care enough to never click on clickbait. And while platforms would probably prefer if people were less stupid and watched videos with informative titles and thumbnails instead, they can't change the fact that most people would just rather watch videos with ShiTty titles and thumbnails, and so they have no incentive to try to prevent creators from creating the thing that people are going to watch more.
So if anything, it would be better if everyone who clicked on a clickbait title for something immediately felt extreme shame and had to sit in a corner for an hour. With the reduced demand for ShiTty titles and thumbnails, the market would take care of it.