I think it was a combination of things. First was the look ... SWMBO and I both liked the look of the homemade units better for something that would be sitting in the middle of our house (at least until we finish the basement, which will be a while).
Cost: It seemed like all of the premade units required several upgrades to get what I really wanted, so it made sense to just order exactly what I wanted from the get-go.
And reliability ... after I thought about it, using a chest freezer with a controller made really good sense to me, because chest freezers are made to run for years, keeping food at 0 degrees, so keeping beer at 35 degrees should be a cinch, right?
And yes, of course, I was intrigued by the possibility that I might be able to make one of these myself. I've been doing small woodworking projects for many years, and am fortunate to have an okay shop ... and to be honest, I'm not sure I would have tried it without that. It was great fun, and I do get a lot of satisfaction from pouring a cold one from something I made ;-)
Sorry for the ramble ... be sure to post picks of your kegerator!