Gmail is not now nor has it ever been free. Everyone pays for it. To your point many people use it and for businesses to contact their customers they have to pay into whitelists for high volume delivery. The costs are passed onto the customers, including those that have never used Gmail. Companies that do not pay into such lists and that have many customers using gmail have to set up careful rate limits which means the emails will not be delivered the same day.

Email marketing and campaign companies pay into these lists and they pass that cost onto their customers as well.

There has never been a email provider that accepts mass email delivery to millions of recipients for free.