i did own once a heavier full carbon board. it was made by Gem, it was a 270cm by 47cm around 70litres, slalom/speed board.
when i bought it second hand i knocked the bottom with hand, it felt real dense + hard as nails.
i used for 2/3 years before finding a starboard 52 that was faster in the chop.
the gem never had a single soft spot after probably 10k use. i think board probably would have lasted at 10 years of twice a week use.
i left it out my back in australian sun and it fell apart by itself after a few years.
the board weighed around 6kg heavy for its size and carbon content.
it costs too much extra for that extra kilo of carbon and besides sales would drop too much, so get back to reality.