Because they’re based on publicly available information. It’s just someone looking at all the public ally available info and saying “well, in my mind, these factors should make this stock worth $30. So if it’s selling for $35, you should sell it; if it’s selling for $25, you should buy it.”

The idea of the stock market is that it’s only fair if everyone’s working with the same information. It becomes manipulation if someone uses non-public info to do that kind of analysis: i.e., “I know this stock is trading at $30 now, but it’s about to announce on its earnings call that it missed its revenue targets by 80%, so it’ll be worth ~$10 when the public learns that. Sell now before that happens!