Because all Wall Street cares about is new hardware. To them that's all Apple is - a company that makes gadgets people buy, and Apple didn't announce any new fancy gadgets today. Of course what they don't get is what Apple announced today will be huge for hardware in the fall and beyond. And a lot of the stuff they announced today could some users who left back to iOS. Especially with 3rd party keyboards, inter-app communication and interactive notifications.
Well for one, since no hardware runs Apple software other than Apple hardware, hardware is pretty important to Apple....and Wall Street. Everything shown today is "free" and so the question is, how much of what was on show today would make you buy Apple as apposed to keeping or prolonging the life of the gear you already have; I fall in the latter category. I guess that is why Wall Street "cares"