I always have fuel to another strip in the 737 and I'm not sure it costs the company more over the years as many times I have been able to hold for 30 minutes ( normally due to TS or single runway ops due wind ) before making a divert decision and then got in to destination while others around me have left for their alternates. Each time that happens the schedule of the ones that divert is thrown out the window and they have an extra burn of five or six tonnes by the time they have diverted, returned to destination, and then picked up their return pax. It's a rare occasion when we can't take extra without offloading pax so that makes it easier.
It normally costs about 50 cents per passenger to take the extra gas minus whatever savings from those occasions when I don't divert when I would have had to. I'm more conscious of efficiency than most I fly with and take whatever steps I can to save fuel enroute and on the ground. Hopefully that reduces my burn a bit as well. At the end of the day different pilots come to different conclusions when making risk assessments. You see it all the time with other elements like how high to fly , whether or not to go around or through weather etc etc. human beings are different, that's just life.