Another unsolicited credit line increase

Time again for my annual credit line increase.  Every year, courtesy of my credit card company, I get an unsolicited increase in my credit limit.  Two years ago they raised my limit to the extent that I could replace my truck if I wanted to.  This year it’s only a few hundred dollars less than the annual salary for my first programming job.  I just don’t understand why they do these things.  I use the card for convenience, not for credit.  I pay the balance every month.  There is no evidence that I’m going to start spending irresponsibly, and yet the credit card company keeps trying to entice me.  I still haven’t figured this one out.