Because introducing an 8GB iPhone 5c and the iPad (4th gen) is the "best work of their lives"
....
Still would like to see product announcements throughout the year, not all at once in September/October.
The iOS ones are now packed into that windows but the Mac ones have consistently have not been. June has lined up with new Intel CPUs for a while now.
January-April has generally been a ghostland though except for adjustmennts that typically should have happened earlier (e.g., 2013: speed bump and price tweel MBP . 2014: retire the freaking waaaaaay old iPad 2. )