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:

https://hackaday.com/2021/11/15/mining-and-refining-pure-silicon-and-the-incredible-effort-it-takes-to-get-there/

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

https://en.wikipedia.org/wiki/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 )

EDIT: Apart from the manufacturing methods, graphene might offer a way to lower the voltage required to operate. Not only that, but electron mobility in graphene is 10 times higher than in silicon.

Good graphene chips might one day require much less power than silicon, and this will be a boon for computationally intensive applications such as 3D rendering or AI.

There's still a long way to go, tho.