Synchronizing efforts has both costs and benefits. Costs are frequently underestimated, especially if you're outside looking in and aren't the one paying them. Communication has the well-known problem of tending to scale like n^2 (though I'm inclined to think it's somewhat more like 1.6, it's still a polynomial growth), and synchronizing two teams often ends up building more than just a leader <-> leader link, let alone three or more teams. It's easy to say "it should be done", it's a lot harder to actually pay the costs. Benefits are often oversold, too; yes, perhaps in this case Google is missing out on some huge opportunity, but even if that is true (which I'm dubious about), it would be the exception, not the rule.

Sometimes the costs still outweigh the benefits, sure, but it's often a more subtle analysis than it first appears. Imposing excessive synchronization requirements is a seductively easy path to some bad problems.

I have no inside knowledge of Google, but the mere fact of their size and general success puts a bound on how much synchronization between teams is even theoretically possible.