[gokr]

A solid good enough reason is because it's fun!

But in the specific case of Nim - AFAIK there aren't that many languages around with a similar set of characteristics. For me the killer is the combination of GC (I am quite fine with not having to bother with memory management), readability, reasonable high levelness including closures etc, nice OO support, extremely good C and C++ interop and really good performance.