It’s easier for the 2pm across the world to be aligned with daytime and 2am to be aligned with nighttime. Otherwise you would have to know the exact geographic location of each place you refer to since 2pm could be morning at one place, afternoon at another and night at another

Also the world completes one full rotation every 24 hrs, with the sun making landfall on one part of the earth before the rest (E.g. sunrise in Japan occurs when it’s sun setting in the western world). Hence it’s easier and more useful to track time around the world by using taking in account the world rotating and sunlight making landfall