Because there are treasures on each OS and to think otherwise would be a bit of the master race mentality.
There are some fantastic navigation softwares available on WinCE and everything that I have used on the tablet has been 2nd rate or at least the experience has been.
Not to mention the library of thousands of programs already made for WinCE that don't exist on the Maemo platform.
I have liked my experience with Linux
but why do so many people actually close their mind smaller than Microsoft just to defend Linux?
Truly, if you can embrace something from all OS's you will be better off for it.
edit: Reading this the next day, this was suppose to come across in a positive way but instead is kind of a-hole like. Just think happy thoughts when reading it and it should read just right.