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.
All platforms are not safe and trusted enough to give our personal information to them like KYC documents. They can be a small or big company, can promise anything but after you submit documents for KYC, you lose those documents to that company. They can have database hack or they can sell user data to another companies for money. It's all things can happen behind the scene and you don't want to see any problem with your personal documents on any platforms.
Such documents can be precious ones for scammers to deep dive into possible ways of scamming you or impersonating you for bad purposes.