|The only valid excuse for this election cycle.|
It's BECAUSE you have bills and mortgages and car payments. Those are all the reasons you should, as a reasonable adult, be sitting down and coloring on a regular basis. Not only is coloring fun (otherwise how would it keep young kids entertained), but it gives you something to focus on, something other than your stresses in life. At the end of it, you get a pretty piece of artwork to put on your fridge (I'm not old enough to not do that); but you have gotten more than that- you have a chunk of time where you couldn't worry about what stuff you could buy as a store brand to save a few cents here and there in order to make the car payment.
Consider the Mandala, noted on Wikipedia that it "is a spiritual and ritual symbol in Indian religions, representing the universe. In common use, "mandala" has become a generic term for any diagram, chart or geometric pattern that represents the cosmos metaphysically or symbolically; a microcosm of the universe." The use of Mandalas for relaxation has been seen not only in these new fad coloring books, but also in therapy and spiritual meditation. Focusing on the image, which is meant to mimic the symmetrical and interconnected nature of the universe. A lot of people I know who color find them very soothing and help with their overwhelming feelings.
I prefer the scapes. Lake shores; images of Disney princesses; I have a bunch of books that are from the "Color the Classics" series, letting me bring to life my favorite classic books. Those make sense to me, they have rhyme and reason, a pattern that I can clearly see and follow through with. I love those.
I think there's also a physically therapeutic aspect to coloring for those with chronic pain in the hands and arms. Just like knitting or other activities that require fine motor skills, this helps to strengthen the muscles in your fingers and wrists to keep you more dexterous.
The flip side of that coin is that, there may be lots of days where you're in pain and those tiny Mandalas or intricate pictures are just too much to ask. There's nothing wrong with a more basic book, although a lot of books have a good variety of skill levels in them so you can skip around from one to another. And if you have some issues with OCD like I do, it can be a good exercise in ignoring compulsions to do every page in order.