Last week ROI on an S9 purchased on shitmain's website was slightly less than a year at .10/kWh. Today, it's over 400 days which essentially means never as difficulty is still rising and bitcoin is still falling. At this rate, it won't even pay to turn on an S9. I guess all the manufacturers pushed their prices high up so they could squeeze the last bit of profit from us miners before the crash.
I don't know how you're running the numbers, but they're wrong. First of all the ROI of an S9 is not anywhere near as long as 400 days, even with bitcoin doing so poorly recently, so that says something right there, that it can keep being profitable even in this environment. Second of all - assuming the difficulty keeps rising and the price of bitcoin keeps falling - yes, the S9 would not make a good investment. However the truth of the matter is that you can't see the future any more or less than the rest of us. You don't know if the price of bitcoin will keep falling, or if it will rise, or what the difficulty will do, etc. If you believe in bitcoin and believe it will make a comeback (which history tells us it will), then you don't base your numbers off today, but what you expect them to be in the future, especially with something as volatile as bitcoin.