It's all about attitude and perception.
Yes, some issues have cropped up on the K1600 bikes. But that's to be expected on a completely redesigned model, from any bike (or car) manufacturer.
But overall, the issues on the K16 bikes have been very minor, and most have been addressed already. I've had enough BMW's over the years to know when there is a serious problem that isn't being acknowledged or addressed (final drives, surging, jumping cam chains, etc.). Sure, a few leaky water pumps, some bum switches, and Bluetooth teething problems can be annoying, but they don't really rate as major failures for the vast majority of bikes out there.
You also have to understand that forums like this are where folks come to get answers to their questions, so you tend to get more problem reports than you get folks just saying "My bike is awesome, and everything works just great!" Those folks are simply too busy riding and enjoying their bikes to post the obvious.
The current business/engineering model for the vast majority of companies is to develop a product, get it out there as fast as possible to start making sales, and then deal with whatever problems crop up. It's a software mindset, where iterations are cheap and easy, but now we see it in vehicles, in computers, in cell phones, and in other consumer products.
It's the difference between Android, who push out phones as fast as they can make them and then abandon them within 6 months for the "new" model, and Apple, who build and refine six different phones in the lab, then only release one model per year, but you know that model is going to perform just as advertised.
There will always be the next new model coming along, so if you wait for that, you'll never buy anything. So you do the research, read all the opinions, both good and bad, and then at some point you make your choice and lay down your cash.
Maybe you have issues that can be resolved, and maybe you don't. But at least you have the product in hand to use and enjoy, instead of constantly waiting for them to get it just right. Me, I'd rather be riding than waiting.
Besides, if you really want a modern BMW that's been pretty much polished to perfection, I hear you can get a great deal on a K1200LT . . .