This is my personal list. Note that I am not saying they are true, but that they are arguments for using windows over alternatives.
1) You don't know any better
2) You don't have a choice
3) It comes included with the hardware (I omit the
word 'free')
4) It is the easier/safer option
5) The hardware/software is better/cheaper
6) It's there/better the devil you know
7) It works.
Note that for a long time I was a mixture of 2&3, then slipped into 4&6 but have been happily running Linux for a bit over a year. By choice. In that time I have considered encouraging others to move from Windows, but for them 1&7 are big arguments. Windows is aimed at them, they don't need any more than that and the options would be a hindrance rather than help.