1) They replace worse and spammy ads.
2) The tracking is really mild. If a big bad government or hacker wants to get dirt on you, they don't dig into FBs tracking algos, they go straight to the ISP or they hack the website you visited. FB also doesn't sell your data.
3) People genuinely find products they like all the time through ads.
4) Whole categories of businesses get a chance for customers to discover their products. Almost every new Shopify store selling cool new products relies on FB ads to get in front of customers. Many really cool useful b2b tech products rely on FB to be discovered.
Advertising isn't magic. It's not mind control. 90% of it is clearly showing a product to the market and you pray you find product market fit.