The point is to have a useful way of getting rid of all the plastic waste we already have and will continue to generate. Plastic isn't going anywhere in the near future because it's a byproduct of natural gas production, which is needed for energy.

Well... It is more that a traditional oil refinery has a BTX section

https://en.wikipedia.org/wiki/BTX_(chemistry)

which produces an excess of chemicals in the process of improving the octane of gasoline

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

and that is where you get monomers like styrene and Terephthalic acid.

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

is another important petrochemical feedstock which can be made from natural gas or other forms of petroleum.