The reason is simple....
There is not another guy that awake itself one morning and was thinking: how do we use tubes in a complete new way in tube amplifier?
His name is David Berning....There is not one negative review of this product and the price is relatively low for the quality, and no more heating and changing tubes each year or so....
Other way to use tubes are obsolete probably, but not more people knows it for the time being.... :)