I doubt the creative pro market (which would be the prime target market for a 17" MBP) is not a profitable one - in fact it's a market much more likely to pay a premium for top-of-the-line equipment.
The problem is that Apple has enjoyed windfall profits with the iPhone and they're now looking for the next opportunity for explosive growth. That isn't likely to come from the Mac business.
Its a question of distorted perspective: if a 17" MacBook took 5% of the Mac business it would, in isolation be a pretty successful product - not to mention the
strategic benefit of keeping Macs in the hands of the sort of power users that influence others' decisions and help bring credibility to the platform. When the
whole Mac range is only 10% of revenues, suddenly the 17" MBP is just a rounding error, and not deserving of investment.
The new 2016 MBPs are definitely the nicest looking "ultrabooks" in the shop, but if you need a desktop replacement laptop, well, there are plenty of large-screen gaming and portable workstation choices in the PC world (not so much with 16:10 screens, though).
I think I could live with a 15" rMBP in "scaled" mode "on the road" in true laptop mode, but the true loss comes when you stick one on an elevator stand next to an external display - with a 17" that gives you a true dual-display setup.
Problem with my 17" rMBP is (a) its on its second logic board - the first one lasted 4 years & was replaced for free, so that's not too bad, but if it goes again its probably curtains. (b) My ExpressCard USB3 adapter and the ScreenRecycler software I use to get 3 screens (Code, Product, Documentation - perfect!) won't work past OS X 10.9. I'm now regretting not getting a TB dock & second TB device for USB3 and 3 screens a couple of years ago.
If I stay with Mac I think I'll be looking at a desktop (when the new ones arrive & if they're any good) + a separate, ultraportable laptop.