With so many programming languages around looking very similar, and realising the enourmous tough challenge to get adoption: why do programmers pursue writing a general purpose language and trying to have it adopted?
Every language has pros/cons and applicable use cases. Think of Python. It is a beautiful language that is high level, uses white space, but requires the python VM and is very slow. Nim has a somewhat pythonic syntax, compiles to C and then binary executables and is very fast with good metaprogramming facilities. That is appealing to a lot of people. I encourage you to read the free chapter of Nim In Action as the author does a good job explaining why.
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.
