Colleges and Alumni donations

My grad and undergrad alumni associates have decided to call me as often as possible, in attempts to get donations.  

I'm always confused by this.  The time period in which I give them money in exchange for goods or services has past.  This isn't like PBS, which I actively use

Target does not call me up to see if I'm enjoying the Gatorade I purchased from them, and ask me if I would like to pay them more retroactively for it

Particularly undergrad -- you guys didn't bother to give me scholarships, opting for more need based over academic based.  Sorry friends, knock on those people's doors