Drying firewood too long drastically reduces Btu content?

One more observation to throw on the "fire": furniture. We purchased sold maple furniture one piece at a time as money was available for our first house. Now, more than 40 years later, the maple furniture is not one ounce lighter. The exterior finish is not a factor because the inside face of the wood is unfinished. Kiln drying could kill spores and remove some volatile material but clearly, some of the old "light" maple firewood sticks are lighter than the furniture.

Meanwhile, if the kiln removed some volatile material, does that mean kiln dried firewood has less heat content?

My guess is slow fungal activity is the main cause of my wood getting lighter after too many years.

 

Burnt some of my to dry firewood, used the pieces that I split last week to check moisture content. It was an outdoor campfire situation where I already had a good coal base.
Low and behold they did not instantly vaporize into a large pile of ash, rather, they burnt quite well for about as long as smaller split oak should.
Shocking!!

I wonder why they say it will leave more ash than normal? That does not make sense to me.