Apple makes one new iPhone a year. So they can spend a whole year advertising it, and building up its brand name and awareness--a name Apple already built up hugely.
All the Android companies come out with new models ever few weeks or months, gadget geeks pay attention, but none of them has nearly the same awareness from the average person since there is no one big phone that you see all the time.
Look when you see people using phones. Especially since 2 years of iPhones looked the same, you recognize them, and it seems like you see a lot. Android phones all look different, it never feels like you're seeing any one of them very much, even if some day (if not already) the total number passes the number of iPhones. So as you're seeing people with phones, it feels like there are more iPhones.
Same thing for laptops if you look in a coffee shop. All the others are a mix of styles and brands, so the Apple laptops stand out.