Many websites we visit and submit our personal information to are most times because we trust them, you can’t just give your personal details to a website you just come across without knowing of their virility with such informations. It may not be easy to know the site that may have sold your data out, but it is also much possible that it may be the most recent one you’ve uploaded your personal information to especially if you have some reservations about them at the time of even registering and providing this personal details. That is why you only give your personal info to where is trusted and have good reputation of trust from existing users.
That's not always the case. Some people doesn't care about these things like KYC and will give out their information when required/asked/needed. While others may hesitate, but still do the same, because they need to use that particular site/service. Tbh, I personally don't trust any centralised exchages but I have accounts that are fully KYC verified. I don't have any other alternatives to do my transactions, so I'm forced to use these (not because I trust them, I don't), not because I trust them but I don't have any other choice.