Good question, to which I don’t know the full answer. But if you look at their motto “move fast and break things”, insistence on pushing new features as fast as possible, and the recent clash and resignation of their CSO, I’d say google are just more mature about security, and understand their products are entirely reliant on trust of their users.

Does it matter? I have a hard time thinking of a worse company to entrust with personal information. The reach of Google makes Facebook look like a joke. At least when it's leaking they're not making more money.

Probably the latter: the larger the value of a network, the more likely it is to attract attackers.