Cost/Benefit ratio is a very big reason why MDF is the most popular. When a MDF enclosure is well engineered and braced it becomes an effective material to control cabinet resonance. Remember that commercial loudspeakers are for profit and MDF is the best option to be used to keep costs down for the enclosure portion of the loudspeaker. Not only in the cost of the MDF itself but also because of its ease of use in manufacturing process compared to more expensive enclosure materials.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne