I mean there is, you send out randomized credentials "please use these for your next login". And if someone lost access to their e-mail address, the proof of ow

I mean there is, you send out randomized credentials "please use these for your next login". And if someone lost access to their e-mail address, the proof of ownership would be the same as it is today (aka sending receipts, keys, etc.). But lets really be honest: These kind of companies dont give two sh*ts about security leaks and GDPR infringements, as is demonstrated almost every other week by news. Privacy or legal compliance is most certainly not the reason they are doing this.