Second strong corporate support, IBM and several other big corporations are behind Linux development and help get it in to the field. FreeBSD doesn't have a large IT services company installing Linux on servers as a part of their consulting business.
So now when I go to look for a server I am going look for a Linux server because I have had better\more experience with it. Basically that which is easiest to use by people without experience will come to dominate. Not through network effects or anything hard to reverse like that but by simple fact that people will start using the tool that makes their job easy. After they have experience with that tool they are less likely to change to a harder to use tool even if it is better(the Mysql effect as it were.)
For me, the _default_ command-line tools are not a joy to use.