While 1440p will undoubtedly make sense for certain cases, it
seems hard to justify such a high resolution within the confines
of a phone, and that’s before 4K displays come into the equation.
While no one can really say that reaching 600 PPI is purely for
the sake of marketing, going any further is almost guaranteed to
be for marketing purposes.
A few readers have pointed out the similarities to the megapixel race in the camera industry, which has thankfully subsided. Only up to a certain point is higher pixel density definitely better.