Yes, what they have now makes money. But their new products keep failing to. That isn't a winning long term strategy.
Their failures are largely because they don't build out and commit to platforms. Every time they have a high profile product or service that gets launched too early, fails to grow, doesn't get supported, and then gets cancelled, they lose credibility with developers. Why be an early adopter for a new Google platform if they aren't going to put some time into making it work and grow? Why make your app work with a Google API that won't last through your product's lifetime? It isn't all about costs and benefits right now, it's about building relationships with people.
How many developers will swarm to any new thing from Apple or Facebook? Tons - and those companies are reaping huge benefits by supporting and growing their platforms.
Google? They're still well respected, obviously - but this kind of thing is hurting Google+, and it will hurt every new platform they launch.