Guys and choking

Hi- I' currently dating and 2/3 of the latest guys I've dated have been into choking. The first time it happened I said no and he stopped for a while but then started doing it again really hard and I didn't like it at all. I've just started seeing a new guy and he started doing it really lightly when we were making out. Why do guys like this?? And is it weird that I don't like it?? Why is this happening so often?!