Actually tell a lie, sometimes I will stay still on an escalator. This is generally because of one of a small number of reasons:

1) I am looking for my ticket/checking my phone
2) I am with friends who do not share my love of running escalators.
3) I am behind an extremely hot girl I wouldn't mind checking out some more
4) there is a lady with a pushchair or pram ahead of me on the escalator.

Seriously those 4 reasons are enough to stop me otherwise *dash* time. Though I have on occasion been glad of stopping behind someone with a pram/pushchair like recently at a local tube station a woman with a pram was searching for her ticket, the pram slipped and nearly pushed mother and baby down the stairs from about 10 - 20ft from the top and about 20 - 30ft from the bottom. I caught both the mother and her pram and helped them the rest of the way, I hate to think what would have happened had I not been behind her.