A Samsung Galaxy S4 next to a smaller iPhone 5 Steve Kovach/Business Insider Why doesn't Apple sell an iPhone with a bigger screen?

iPhone owners want to know.

Partisan Apple bloggers like Horace Dediu want to know.

Apple shareholders want to know.

The question gets at a larger one: Why does Apple only come out with one kind of iPhone at a time?

Back when Apple's biggest business was iPods, it sold several different kinds of those. iPod Classic. iPod Mini. iPod Shuffle.

Samsung, meanwhile, is starting to kick Apple's butt in terms of market share AND profits by selling all sorts of Galaxy phones.

What is Apple thinking?

Last night at All Things D's D Conference, Apple CEO Tim Cook answered some of these questions.

Paraphrasing, he said that Apple sold different kinds of iPods because the market was big enough that it made sense to build different kinds of gadgets for different people and different needs.

So far, Apple has tried to best suit all people with all needs with one phone model: the very latest iPhone.

That may change in time, said Cook.

One way it may change is that Apple may someday make a phone with a bigger screen.

It hasn't so far, Cook said, because "a large screen today comes with a lot of tradeoffs."

Cook said that the bigger a screen gets, it gets darker, it uses more battery power, and it's less likely to show colors correctly.

Cook said Apple customers want Apple to weigh all those variables "and come out with a decision."

For now, Apple's verdict is that a slightly smaller screen is the best answer for the most customers.

Cook said that as those bigger screens require fewer tradeoffs it will be more likely that Apple installs them in its phones.

At least, that's our understanding of what Cook said.

You can watch him speak his own words in response to these questions, here: