Honestly, I often hate how people ask "why?", and don't understand how "for fun" is a legitimate answer. I get it for work or other things, but hobbies? We do lots of things for fun! Humans were born to play, just like every other animal. It's how we learn and explore the world around us.
And frankly, to quote Knuth
> In fact what I would like to see is thousands of computer scientists let loose to do whatever they want. That's what really advances the field.
This is true for any field, or any project. We're creative creatures. We dream and explore. Major changes almost never come from doing things the way they've always been done. A lot of times "just because" gives you the freedom to try new things and challenge those paradigms. Weirdly, if you always have to justify everything you slow down progress.