Something, something, "put the armour where the holes aren't."
If you are selling a lot of phones and tablets and laptops with your apps and platforms as they are, you don't want to invest billions in making them better just to make your existing customers stop complaining. They bought your product anyways, clearly whatever they're complaining about wasn't a deal-breaker.
You only want to invest in your own apps and platforms in areas where improvements would drive meaningful business outcomes. So you need to look at features that would cause someone who would otherwise buy a Samsung phone to buy an iPhone. Or you need to find people who didn't but an iPhone or iPad or AppleTV or OS X laptop and figure out if there is something that can be added to the product to get people to switch.
In the case of a dominant player like Apple, those are hard to find in the mainline product. Big new sources of revenue are most likely to come from entirely new product areas (thus their investment in phones, watches, tablets, and set-top boxes) or from going down-market and making commodity products.
They're allergic to cutting margins to the bone, so we're left with trying to find new markets, and that is why they invest so much in an automobile skunkworks while being much more careful about investing in the products that are already successful.