Longer name? micro is only five letters long, and nano is four. Yes, it's longer than nano, but it's only longer by one... Care to elaborate?
echo 'alias m="micro"' >> ~/.bashrc
A person who knows and likes the program can do that, but the default name is a drawback for adoption. Nano is shorter name, using it is user-friendly and it already is on almost every modern Linux installation. So micro has a tough rival to beat, and it seems to be an "uphill battle".