Google says "Gmail hasn't mined data for commercial purposes for half a decade now." just like how cops says "We have investigated ourselves and found no haven't found any faults"

Specious....

The difference being one has deep pockets and would set a world record with a billion-person class action lawsuit, if they were lying.

Then why is gmail still free?

Gmail is still ad subsidized, under the sponsor tab or whatever. You don't need to mine emails to show someone adverts to click on.