Think about Apple's Macbooks, I'm pretty sure that they are status symbols as well.
People who buy devices as status symbols, to show off how much money they have, are not the target audience of this project. They usually do not care about the benefits of open source and sustainability anyway. This project is about recycling old phones, which would be insecure/useless without an alternative operating system.
> Another driving force is that a smartphone made a decade ago would simply not be able to use many of todays apps because it is missing certain sensors.
That is right, but it is theoretically possible to get the devices from a few years ago running for five more years, and the devices created today for the next ten years.