You will once you grow up ;)

(See what I did there, putting a wink emoji after that sentence?)

That's not an emoji.

The shortcomings of pure text for online communication have been recognized since forever (mainframe-based forums and Usenet in my own experience). Emoticons were invented to provide some of the visual/tonal/emotional cues present in RL conversation but missing from text. Emoji are the natural evolution of emoticons, providing a richer vocabulary and often requiring less interpretation. Is it really hard for you to understand why "grown men" might want to communicate in something other than a flat, dry, emotionless format? Do you not see the problem with that? Because that would be :(

Emojis sometimes make it a lot easier to convey sentiment than text. Also, "grown men" are allowed to have fun.