The DS and the Wii are completely 2 different systems. Porting is not as easy as it sounds. It takes several hours of hard working(I'm not saying 3-5 hrs, I actually mean 50hrs+ depending the skill, number of ppl, and the target console), remember people are doing these stuff for free and are being developed on the spare time of people. They both have different types of CPUs and GPUs so making a port would be pretty hard.
Think of it like this: Trying to run an apple Mac program on a windows Desktop PC... different methods and languages are used which the windows Desktop can't recognise. The point is, it's a lot of work to port anything and you want them to port a whole emulator to Wii..