Huh? Err, I've used IceWM in the past in debian without having to try hard at all (apt-get install icewm... wow... that was difficult!) and I'm currently using ion3 (guess how I installed that... oh, yes, apt-get install ion3)... Of course, synaptics can easily be run in any of the window managers - the libraries for it will get pulled in on its installation anyways. If people are switching window managers, then they generally can still find applications.
To you that is no problem, to another person it can take hours to track down everything they need.
Can you clarify which packages you're suggesting are vital for using IceWM (as the example that you provide) that are not in the Recommends or Suggests lists for IceWM?
There are no packages needed for IceWM to be installed and work, there are just packages needed to use the operating system if you want more than just a barebones window manager. Remember, we are not all developers, to most people the OS is a tool to be used for other tasks.
"Everything should be made as simple as possible, but not simpler." Albert Einstein