They're too small. Any project requires a certain amount of headspace. I just don't have enough to work on two hour projects that may or may not lead to something else. It just sounds like a pain-in-the-ass.

Also, being a good developer doesn't mean I know how for loops and basic OOP works -- it means I know how to build and organize non-trivial projects that require thought and care. Having me work for two hours on something random won't tell you anything about this.