I think even if 99% of google users have strict privacy, this tool is still worth it for data brokers as they can run email lists of millions of users.

And every data about a user that can be connected to the rest of the master data is gold as its all about the network effect.

edit: https://imgur.com/a/o2petUC

here is a good example. The white box is from a publically available dataleak of a site called SexDating.se. its 10 years old db. but still i managed to extract the name of the person even though the original DB had no identifiers apart from this gmail.