Even with fractional shares, people (poor investors) still prefer to buy shares whole. And it can make tax-time a bit simpler I suppose.
That said, splitting the shares allows more contract equity to come in because those priced out of the higher-stakes derivatives can now bite a little without having to play at nose-bleed risk.
Yes, I know someone is going to point out that the poor-man can just do spreads to get around that, but spreads are not risk-free and have their own risks, particular with equities like Tesla, which has many already existing examples of spread disasters gone wrong...