You are correct that oil changes are inexpensive and frequently offered as loss leaders, however:
A - I buy my premium oil by the (several) case when it is on sale, same for premium filters. The oil and filters used by cheap oil changers are not of equal quality. B - I can change the oil at home in MUCH less time than it takes to travel (more $ for gas) and wait for someone else to do the job, according to how busy they are this wait is often not insignificant. C - By doing the work myself, I can do it at my convenience and when it should be done at not when I have the time to schedule the chore into the time the oil changer has available. There is never a line up at home and I am open for business any time I want to be. D - I do not change my own oil because I am saving money (which I do, but not a substantial amount). I do it because it is easier, quicker and more convenient. It is usually combined with other preventative maintenance work which I do not trust an oil changer to perform. I did make the mistake of going to an oil changer (once) and because I thought it would be convenient (long story), had them check and change the manual transmission oil and top off the OD. I neglected to get a firm price quote for this service and ended up paying a huge amount for the trans service and the trans oil AND had to show the kid how to do the job as he did not have a clue.
Self sufficiency is an attitude and a lifestyle which cannot be explained to people who do not share similar feelings. Different strokes for different folks, as always YMMV