Thanks everyone, for their considered responses. I feel like I have a really suitable answer to my question of "How do I explain this to someone outside of our sport" - and that is the concept of "sportmanship" or "fairness".
For me, this is the first sport I have attempted in which I compete as an individual. While sportmanship is almost implied in many team sports, this wasn't as obvious with cycling. Now that I am reminded of this most basic of courtesies, it justifies a great many rules of thumb and cycling etiquette.