There is a difference between making people "feel better" and treating their medical problem.
I would "feel better" if I got a massage twice a week for a couple months, too. And let's not forget how important it is for the patient to BELIEVE you are doing something beneficial to them, whether or not you actually are. Belief is powerful. There are three words you'll never hear chiropractors say: "I don't know."
Chiropractors will always tell you 'Oh, I know exactly what the problem is. Its just a matter of your whatchajigger being misaligned with the whatchamacallit causing disharmonious regulation of the humor, thus making your "core" weak (whatever the hell a "core" is). We'll have you fixed up in no time.'
This is MUCH more reassuring than the honesty that doctors are trained to have (e.g. I am not sure what's wrong with you, but we'll start treating the most likely explanation for these symptoms, and if that doesn't work, move on to the next most likely explanation. Don't know when you'll get better, could be tomorrow or never. Just can't say for sure."
Wow, that sure does instill confidence, doesn't it? Makes you just want to leap into a chiropractors office, even though its the most honest answer.