That's because if you don't use your trademark, you lose it. There's no equivalent to "Oh, I used the name in a little-known paper I wrote and now I can sue you." If nobody knows about your trademark, you probably don't own it.
Technically it isn't the lack of use that will kill a trademark, it is the lack of defense or people using it as a generic term. The need to defend actually causes most of the trouble with trademarks since you really need to be a little more agressive than you would like.
