Programming is unusually accessible compared to other skills. If I wanted to learn how to raise farm animals, where would I start? A person needs only a few common things to try programming: an off-the-shelf computer, maybe a book, and these days an Internet connection. After that, they require only the traits common to any other hobby, such as free time and enough imagination to figure out what is going to be built. (I'm glazing over a few details of course, such as the fact that knowing how to type would certainly speed things up.)
Programming is also an unusually marketable hobby skill. With many hobbies you can invest a lot of time and effort and produce beautiful things, but that's liable to only gain you praise; in programming, it can gain you a really good job. This is a pretty smart investment: for a modest expenditure yourself you might net a high income so it should not be surprising if people often teach themselves.
Besides, when I hire someone I like seeing evidence of side projects that reveal a certain passion for doing good software work. I wouldn't hire an artist or designer without seeing a portfolio either, and software has a lot of things in common with art and design.
Programming is also an unusually marketable hobby skill. With many hobbies you can invest a lot of time and effort and produce beautiful things, but that's liable to only gain you praise; in programming, it can gain you a really good job. This is a pretty smart investment: for a modest expenditure yourself you might net a high income so it should not be surprising if people often teach themselves.
Besides, when I hire someone I like seeing evidence of side projects that reveal a certain passion for doing good software work. I wouldn't hire an artist or designer without seeing a portfolio either, and software has a lot of things in common with art and design.