Why do men always insist on buying the drinks on nights out?

When ever I go out with my male friends they always buy my drinks, I don't even bother taking money anymore. I get so many drinks I don't even get to drink them all. Used to try to pay for myself but now I don't even bother because I always get one of guys follow me to the bar and insist on paying. They also always pay for my taxi and food after too. They deny having any sexual intentions so I don't really get it?
Why do men always insist on buying the drinks on nights out?
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