Does Apple do research in biotech (Alphabet's Calico)? Are they developing drones delivering wireless internet to the world (Google's Skybender)? Do they have an investment arm (Google Ventures)? Did they start an ISP (Google Fiber)?
People see Alphabet's increasing outreach that almost seems ludicrous. Then they compare this with Apple who seems to have been doing iPhones and iPads for 6-10 years, and doesn't seem to be interested in anything else (though this is slowly changing with Apple apparently getting into home automation and self-driving vehicles). It doesn't matter if it is true or not. This is what people perceive. This is what makes them value Google more than Apple. For all we know smartphones and tablets could be disrupted by another technology (the same way PCs were disrupted by phones and tablets) and Apple may not be ready for this next tech disruption, while Google is placing bets in many other markets.