Why a cook specialty authentic mexican food needs two years prior
experience in order to perform duites?

That's just how it is.  Line Cook positions usually require 2 years
experience, and Head Cook positions usually require 4...

The Department of Labor considers restrictive to require two years
experience. They say that a cook with 1 year can perform in a
resonable manner the duties.

In most locations, an employer is free to set whatever experience
requirements he wishes. If the requirement is unreasonable, the
employer may find that he isn't getting any applicants, and he'll need
to revise his expectations in order to fill the job opening.