While silicon is abundant on Earth, monocrystalline silicon is incredibly hard to produce. You need to use either chemical purification methods that use silicon compound gases, or to use a slow process that starts with a crystal seed to slowly grow giant rods of pure silicon under a chamber filled with argon gas, and many things can go wrong.

Semiconductor-grade silicon needs to be 99.999999% pure to guarantee good yields of microchips.

More on this process here:

hackaday.com/…/mining-and-refining-pure-silicon-a…

OTOH, there are more (and cheaper) ways of grafene production:

en.wikipedia.org/…/Graphene_production_techniques

(On a related note, you might be interested in the history of the transistor to know the arduous path that humanity took just to get where we are )