The letter "M" stands for 1,000 in the lumber industry, so "MBF" is the abbreviation for 1,000 board feet. Think Roman numerals for 1000.
To answer your question, if you are in the business, I guess mbf is a more common expression than the words that it represents. If you are talking speed, mph and kph are commonly recognized. Nobody questions psi when they read the label on their tire (while in the USA, the last bastion of the English measurement system). So... kindly don't get so pissy about folks using a common expression that you just don't happen to be familiar with.
Here's a question for you! Why are ALL the movie credits displaying the year it was made in Roman numerals? Even the Romans don't use Roman numerals anymore.