For me, it's because the challenges are complex and the problems lend themselves to being broken into manageable pieces. If I, instead, wanted to build a space

For me, it's because the challenges are complex and the problems lend themselves to being broken into manageable pieces. If I, instead, wanted to build a space shuttle, there are some real barriers to entry (not the least of which is the few millions needed to get me some rocket fuel and so forth), but with computers it's just me, the debugger and vi. I can do anything I want, limited only by my skill and imagination. I like those kinds of limitations...