They're assuming your complaint about spending a few extra seconds activating the pump implies you're then climbing back into the vehicle after starting the pump, as a few seconds on a several minute encounter with the pump really isn't that much time.
Also, FWIW its not that crazy about asking about a car wash when its freezing outside especially if you're in an area where they salt the roads a lot. From what I understand a lot of people will do a lot of undercarriage washes when things get salty. I don't live in those areas so I'm not the best to offer advice in that, but I do know briny water and metal aren't good for things you want to not have rust to nothing in a few years.
A few seconds is plenty of time when it's being rudely wasted and I'm freezing my ass off.
I agree, it's important to wash the undercarriage when there's salt on the road. However, I would never get a car wash at any old gas station, the risk of swirling or scratching my paint is too high. On top of that, who knows if these bottom-barrel gas station washes even clean the undercarriage effectively, or even at all.
Oh and of course there's the risk of accidentally pressing the wrong button, being charged for the car wash, and having to waste more time getting refunded.
