MDF is an engineered product comprised of homogenized hard and soft wood pulp, binding agents. It is dehydrated and pressed together to create a material that is of higher density than fiber board.
The amount of sawdust needed to create a sheet of this stuff is astronomical compared to the output, not to mention the manufacturing process being very resource intensive. You also cannot just take bags of sawdust from the wood mill - it must be macerated and ground to a very fine dust with roughly the consistency of flour.
The main advantage it has is that it is heavy (to weigh down furniture) and very easy to cut with bandsaws, mills, lasers, etc because of its uniform distribution of its constituent parts. It’s also good for applying vinyl wraps and edging which is one reason why arcade cabinets are often made from it.
All this for a product that is roughly the same price as A cabinet-grade ply:
MDF 3/4” x 4’ x 8’ for $52.98: https://www.homedepot.com/p/3-4-in-x-4-ft-x-8-ft-MDF-Panel-D...
Radiata Pine plywood 23/32” x 4’ x 8’ for $55.98: https://www.homedepot.com/p/23-32-in-x-4-ft-x-8-ft-Cabinet-G...
