Carbon fibre is made by drawing a polymer precursor into filaments and heating them in stages until almost everything but carbon is driven off, leaving aligned graphitic chains. It is energy-intensive, takes hours, and the precursor is itself a specialised product — which is why capacity is added slowly and why fibre grades are not interchangeable.
For aerospace the fibre is usually supplied as prepreg: fibre already impregnated with a precisely metered amount of partially cured resin, shipped and stored frozen so it does not advance before use. That frozen shelf life is a real logistics constraint, and it is one of the practical differences between aerospace and wind, where dry fibre infused with resin at the mould is more common.