Google doesn't need to charge for the basic stuff... they already make money hand over fist off of you using their stuff... If they get away from their current model, it'll kill them. Google makes money off of people using their services. It is their massive user base that advertisers and marketers covet. If start charging for stuff that people had been using for free, like Google Photos (which is really just an extension of Google+), people just go off and find another free offering, and their user base shrinks...
And they lose money.
Put out of your mind that Google is somehow giving away services, or losing money by offering them to us for free. It is a simple exchange.... it's similar to broadcast television.... sure, we can watch it for free, but they recoup those costs via advertising dollars from commercials and product placements. Google does the same thing....and it makes them a filthy amount of cash.