Why do some Texas Hold'Em players go All In before the flop?

Often its the right move to make.  Other times (often when it isn't real money), players don't care.

Often when these tournaments are televised they have whittled down to the last three players and it’s late in the game. The forced mandatory bets (the “blinds”) have increased over time and by the late stages they represent a significant portion of each players total chip stack. In order to keep in the game, and sometimes regardless of the hole cards, a player will shove all-in and put the pressure on the opponents to decide if the cost of calling the aggressive bet is worth that much equity.

You might as well ask why do people do anything.

Often its the right move to make.  Other times (often when it isn't real money), players don't care.

Either to drive somebody else out of the hand, or because they're bluffing, or some other reason.

Isn't it obvious

I've done that many times for no reason. Luck was not on my side, unfortunately.