Loss of grasses left topsoil loose and unprotected.
»
high winds frequently blew on the great plains.
»
valuable topsoil needed by farmers was thus blown away.
»

The logical continuation of this chain would be:

Millions of acres of productive farmland became barren desert.

Without grass, the land had no protection from he winds, which blew away the fertile topsoil. And resultedly, we receive a deserted area, with no plants growing there.

the answer to your question is a because laws act as guidelines as to what is accepted in society. without it there would be conflicts between social groups and communities. it serves as a norm of conduct for citizens.