Because it is not conducive to maintaining any kind of organized group of human beings.
The idea that "life is meaningless" means that society cannot rely on you, because you'll do whatever strikes your fancy, whatever the consequences.
Worse, it is also a philosophy that contributes absolutely nothing to actually understanding the nature of the world, which is kind of the point of philosophy.
In short, nihilists are utterly useless, to themselves and the world. On the upside, they won't care.
The idea that "life is meaningless" means that society cannot rely on you, because you'll do whatever strikes your fancy, whatever the consequences.
Worse, it is also a philosophy that contributes absolutely nothing to actually understanding the nature of the world, which is kind of the point of philosophy.
In short, nihilists are utterly useless, to themselves and the world. On the upside, they won't care.