I suspect (without hard evidence) the sticking point is regulatory. Being in the business of allowing private individuals to move money around opens a company

I suspect (without hard evidence) the sticking point is regulatory. Being in the business of allowing private individuals to move money around opens a company to massive scrutiny. Scrutiny Google probably doesn't want, especially if it gives the government an excuse to snoop around in Google's related enterprises. At the revenue point of the service, let somebody else be Uncle Sam's punching bag.