Why the number of temporary workers is on the rise? Discuss main reasons?

Temporary workers:
Temporary workers are those workers that a company can hire to perform a certain task along with in a defined time period. Temporary workers are mostly consultants that move organization to organization to perform assigned workers.

Reasons:

1. Now-a-days; overall world is suffering from financial crisis, most of the companies have frozen there hiring, only in case they required a resource they are searching for a temporary worker for a specified time span to perform a specialized task and they just pay him for in which period of time.
2. Temporary workers are mainly consultants that have expertise in a certain field and they are considered specialists in that field.
3. Employer doesn't required to train the temporary worker.