There are other things to consider.
A bandsaw mill is far more efficient, but needs to have water injection to cool the blade.
As Kevin says, production is part of it, but so is access. To use a bandsaw, you need to be able to reach the log with heavy equipment, and have the open space to set it up.
With a chainsaw mill, I can go to the log, in the woods, and mill it and carry the boards out. This allows me to go into the woods and/or over septic systems that would preclude the use of heavy equipment.
At the moment, I'm scrambling to build things out of my milled Red Oak and Hickory before it goes bad, and have Walnut, Ash and Oak logs I don't have time to mill!