iPhones are popular because of a monolithic product that doesnt try and depart from the core brand and feel of the OS with manufacturer quirks (ie. Why Samsung and Huawei feel so different). Their marketing is very much the reason:

iPhones are pitched and priced to appeal to the highest social status possible, the rest bleeds down from there.

The percentage of people who buy iPhones specifically because of debated security benefits is substantially smaller. People who may have heard this but dont know/understand it will find it simply reinforces their existing preference for an iPhone on the earlier grounds.

no it's marketing