Because I can.

Everyone always tells you “don’t reinvent the wheel.” Use existing frameworks. Don’t waste time building what already exists. And they’re probably right for most people, most of the time. You aren’t going to do it any better than x engineers.

But sometimes you need to prove to yourself (and any future potential employers) that you can actually build the wheel. Sometimes the best way to understand production-ready software is to build it yourself, exactly the way you want it to work. Sometimes problem-solving IS the point.