There are three main reasons:
1) People who commit belief that commiting suicid is the right thing to do commit suicid, therefore there aren't any people left who belief that commiting suicid is the right thing to do. Add a little bit of Darwinismn and it should be clear that it is programmed into our mind that suicid is a bad idea.
2) Because to many people in the Middle Ages thought that going right to haven by commiting suicid is a good idea, the church outlawed it. The pope said that everyone who commits suicid goes to hell. Problem solved.
3) Humanismn has as its agenda that the human life is more valuable then any abstract ideas.
Therefore suicid and Self-Sacrifice is not popular in our western society.