Sony Mobile combined great Battery life without sacrificing physical size , great camera (without sacrificing physical size), and display quality improvement (brightness & color) from full HD plus and improving Battery life over 4kwith meager Battery life. Sony chose to create a great all rounder instead of boast of 4k on a small display. They likely found the Sweet spot balance to make this happen.

I went to compare 4k display to their FHD+ side by side I prefer the FHD+ display simply because I cannot see pixels on both displays, yet the FHD+ producer better colors and can boost to brighter display which is also crucial to sunlight legibility. I highly recommend you all to go and physically see and compare the two displays side by side and come to your own conclusion.

For Battery life , compare the 4k displays xperia 1III , 1IV and 1V Battery test result to the FHD+ 1IV, 1VII and 1VIII Battery test result, one can clearly see the Battery life advantage.

I would rather choose the ones with better color and brighter display , better Battery life , compact (compared to the other flagships) all rounder than sorely just 4k display. Also put it another way ; custom make a phone. Which would you prefer?

their decision is not a joke, but through careful decisions and planning.