why does no one play e5?

play more

Because people have different styles of playing.

When someone plays e4 I always play c5

It really depends on your opponent on what style he/she wants.

To answer your question, jus play more

you obviosly do

It tends to come in waves.  Only one of my last 5 opponents responded to my 1 e4 with 1 e5.

But don't expect a majority among strong players. 1...e5 is the 2nd most common response to 1 e4 after 1...c5 among masters.  Then there are a lot who like 1...e6 or 1...c6. 

1....e5 is played at all levels. I play Sicilian because it scores very well for black and it has served me well. I don't have to study defenses against the King's Gambit, the Ruy Lopez or the Italian Game. Of course, you do have to study all the Anti-Sicilians, but, if you've done your homework, the Anti-Sicilians don't score as well as standard responses to 1. e4 c5. I've been learning the Modern (1....g6) as a change of pace.

I haven't seen much 1 . . . e5 lately because I've been focusing exclusively on playing 1. d4 to learn queen's pawn openings.

because most people revise only the e5 lines. but some times people play things that are equally good  or even better. the french, caro kann, sicilian. are examples.