There is. It is called GDPR.
Plenty of companies have been fined for leaks like this.
Some countries also have whistleblower bounties but, as you might expect, there are some perverse incentives there.
How does security research like this work out in practice, in the EU?
I read a lot of vulnerability writeups like this and don't recall seeing any where the author is European and gets a better outcome. Are security researchers actually compensated for this type of work in the EU?
How about fining individual developers with poor coding practices?
Also, it needs your company's business model to not be selling user data. That's why American companies find it hard to comply with.