John, I am talking about factories turning out hundreds of guitars a day, not individual luthiers producing one or two a month.

A constant radius fretboard in a factory set-up like Martin or Taylor is produced in a matter of seconds by feeding it through a shaper (or spindle moulder as we Brits call it) with the appropriately ground cutter in the arbor.

You can't make a compound radius fretboard as fast as that.

Hence the reason why factories prefer constant radius fretboards.

(And also, of course, because it makes the installation of the frets so much simpler for semi-skilled operatives).