WHAT HAPPENS WHEN GOOGLE OFFERS Your PRODUCT FOR FREE?

Regarding the "you get what you pay for" argument, in this case what you're paying Google is not "zero". You're paying them in data - specifically what they can learn about your email usage patterns. That might well be very valuable to Google, so they'd be happy to give you an awesome product for "nothing".

The HN mantra of "If you're not paying then you're the product" holds true in this example.