I am a blogger and I just love writing so much that I'm quite sure I would do it even if I wasn't getting paid for it! I guess it all comes down to whether you love it or if it's your passion or not. It's so much harder to try and accomplish something when you have no actual interest in the subject.
I have an actual interest in writing, but I find it to be too tasking. I try to write as much as four times a week but I always try to look at how I can earn from it. I have been a columnist, for some local publication, before.
If you're predominantly thinking about how much you can earn from writing, and not more focused on the writing itself then I can see why it would seem 'taxing' to you. Try and not think about that side of it, and rather only think about the joy of writing. When you follow your passion the profits follow you.
SEO writing isn't that hard if you start small. If you have to write a 500 word article that only needs 2 keywords mentioned twice.....that's pretty easy. When the density starts to get higher, that's when it gets more challenging.
I think I've been a writer almost all my life, the only difference being that I tend not to take myself seriously at times. It is easier and less tasking for me, when I am writing in prose and not necessarily with a topic in mind.