Someone asked the above question, and whilst it seems facile, I couldn’t resist…
Short answer: because there's no profit in it.
This quote from Tim Cook (emphasis mine) may seem to contradict the shorter answer, but bear with me:
"Stock price is a result, not an achievement by itself. For me, it's about products and people. Did we make the best product, and did we enrich people's lives? If you're doing both of those things–and obviously those things are incredibly connected because one leads to the other—then you have a good year."
— Tim Cook
Which presents three questions about the option for Apple to develop a Printer:
To the three questions above, I'd answer: No, No, and No.
Keep in mind that Apple doesn't do thousands of products. It chooses very carefully in order to maintain focus on a small number of products. That's just how they've chosen to operate. Given their chosen business model and go-to-market strategy, they really can't afford to dilute focus by also developing a nice-to-have product. Each additional product they choose to develop also has a cost in terms of diluting focus.
Apple said effectively the same thing in the WWDC2013 intro video, which seems to have gone from their YouTube channel. (I’ll post a copy here for educational reasons, until someone asks me to take it down!):
If everyone is busy making everything then how can anyone perfect anything?
We start to confuse convenience with joy, abundance with choice.
Designing something requires focus
The first thing we ask is: what do we want people to feel?
Delight. Surprise. Love. Connection
Then we begin to craft around our intention.
It takes time…
There are a thousand no's for every yes.
We start over
Until everything we touch enhances each life it touches.
Only then do we sign our work:
"Designed by Apple in California"