It's prestige more than anything and they tend to lean toward research and academia, at least where I live. Social workers who are licensed to practice therapy have a Masters in Social Work and can bill insurance companies. Same with Masters level counselors. I've seen both a psychologist, social worker and an LMHC and have found the letters after their name have no bearing on the quality of their work. My best for T has been an MSW.

I'm in a psychology masters program and I've wracked my brain trying to figure out the purpose of the psych d or phd, since they really don't net much more money in the end. A masters level psychiatric nurse makes more and can prescribe meds.