You change your own oil, but don't rotate your own tires? Changing tires seems like the easier of the two, especially if you already have everything to lift the car?
"Easy" in terms of complexity, yes. "Easy" in terms of strength required to mount and dismount wheels (especially the big heavy ones on the SUVs so many folks have these days), no.
I do most of my own maintenance on my cars for two reasons. I kind of like doing them myself, and I can make sure it's getting done (and done correctly). Not saying all shops are like this, but I have seen some shady and damn right ignorant practices going on. From not actually doing the service you paid for, to totally using the wrong oil, or over tightening lug nuts, or worse not tightening them enough. My aunt had a tire go rolling down the road after she pulled out of the tire shop she just bought the tires from.... I get it not everyone wants to do it themselves, or they don't have the tools or the space to do it. Just verify the work is being done right is all...