A lot of players play a setup similar to their main response to d4 in order to narrow their rep. Maybe the positions are objectively a little inferior but it gets the player a position they know and are comfortable in while at the same reducing the theory they need to know.
c4 e5 is playing the sicilian an extra move behind
most e4 players do not want to play the sicilian so I doubt they would do it as black either.
I would far prefer the KID to behind a move in sicilian.
so why do you think c4 e5 is so good for black?
It is a matter of choice
Many grandmasters (e.g. world champion Viswanathan Anand) have consistently played 1.c4 e5 with Black. Others favour the KID or other defenses : Hedgehog (with b6), symmetrical English (1.c4 c5), Pseudo-Nimzo (with Nf6 and e6), Pseudo-Grünfeld (with Nf6 and d5), Réti (with e6 and d5) or Slav-like (with c6 and d5) defenses...
There is ...