There are many videos from Petro-Canada and Esso promoting the advantage of synthetics in cold environments.
The Chevron video showed that there is no advantage using 5w40 in applications where 15w40 will do.
Oil companies make their money when you pull up to the pumps.
Who then is driving the synthetic label? OEMs require a lubricant to meet a specification, not a formula.
That leaves the retail market, who likely pay for the "as seen on TV" infomercials.