Also, MDF is very heavy and its dust is toxic to breath. The weight makes it difficult to work with, much more difficult than other sheet goods. It dulls and gums up tooling quickly. Plants who machine it, need very elaborate dust collection systems. It may be less expensive, but the costs are a bonus, and not the primary driver for using it. There is a great deal of ignorance with regards to MDF from folks who concentrate on costs more than functionality.