I'm with the others on my main reason being the quality of the guides and the knowledge they bring to the table. I have done 12 Rick tours as well as 13 Road Scholar tours and now coming up on my 3rd Seymour Travels tours. The thing I've enjoyed most is the education from the guides. Generally excellent!
But also:
When I started doing Rick's tours in 2013, I really had not much familiarity with doing public transit. I've never lived in a city where that was available so was apprehensive. One of the things that attracted me was either written info or a youtube video saying the guides teach you how to use public transit. Yes, they do. And my guides have always made sure I understood what to do! Gamechanger for me which might not matter to someone used to a big US city. Now I can hop on the Metro in Paris with confidence that I am standing where I won't annoy the locals and am aware of where pickpockets might be hanging!
I also like that you don't waste time figuring things out. Back in the olden days (pre-computer) I did some travel in England and that was still when you rocked up to a train station Tourist Information kiosk and got accommodations from them. That took so much time! With Rick's tours the bus drops you as close as they can to your hotel and boom,you are ready to start touring because you are generally in the middle of everything.
You can travel more cheaply without a tour. At this point in my "tour" career, hahaha, I combine independent travel with tour travel. I feel like every penny I spend on tours is well worth it for me.
BTW, I don't think you ever know if you are a "tour person" unless you do a tour. I am definitely NOT a big tour group person which to me is an entirely different mode of travel than a smaller 24-28 person group.
BTW, if you are ever in CdA on the 1st Saturday of a month, we generally have a local meet up and everyone is invited.