Well, i like the "Why" part of that question , as it gives me a chance to know about other beliefs and how their followers perceive those beliefs.
Religion has always been an interesting and mysterious thing to me as a teenager growing up in a Muslim family in an Arab country.
The way my mind works; i can't just take anybody's' words for something without it sounding LOGIC to me , having friends in school who had different religions "Mostly Christians" made me think about that a lot and try and seek knowledge about it .
Does God exist ? if he/she Does then why he created us humans ? why there are so many religions ? which scripture or interpretation thereof is right ? and why it is right ? That lead me to do a lot of research, reading and discussions with followers of many religions (mostly Jews , different denominations of Christianity and muslims), i kept my mind open for everything that's out there hoping for that thing that makes sense to me.
I was very lucky that Arabic was my mother tongue to be able to read the Muslims scripture "Quran" which is only available in Arabic and there is no other versions of it in any other languages (every translation out there claims that it can't be 100% accurate)!!.
in that journey seeking the truth , i found out that only very few that can really discuss religion in an open-minded way without judging others for what they believe. and most people (no matter what their religion is) get really aggressive when it comes to criticizing their beliefs even for the sake of argument and without being disrespectful or anything, it's just the way my mind works , i'm a critical thinker and the only way to be convinced is logic .
looking at how complicated and utterly precise and perfect human beings and all other creatures of this universe are made , this can't be made by chance!! nothing is out of order and everything is governed by extremely precise laws , I've studied physics , biology , chemistry and Mathematics (I'm an engineer btw) so there has to be a creator of all that !! ,so how he/she looks like and why we were created ?
after research , i was down to Judaism , Christianity and Islam , those are the religions that claim there is GOD and they claim to have teachings and scriptures sent by God to humanity .
Apart from stereotyping about those religions , i was seeking the truth about them , and why people follow each of them ?
So , i found that Jews do believe in Moses and the Torah but not Jesus nor Muhammad , Christians however do believe in Moses , the Hebrew bible (the old testament ), they also Believe in Jesus but Not Muhammad , Muslims however do believe in Moses , Jesus and Muhammad !! but how is that possible?? how do Muslims believe in Moses and Jesus ??!! in fact i found out that in order to be a Muslim believer , you Must believe in all prophets and scriptures sent to humanity by its creator ! interesting, i thought .
i realized that most of the teachings of the three religions are the same ! however , everything is very detailed and clearly explained in that miracle book called (Quran) .
And the reason i called it a miracle , is that it has survived for more than 1400 years so far with Not a single second version of it , not a letter changed , not a second story , NOTHING ,one 600 pages book had not been altered in any way for all those years . That was not the case with the bible when i looked .
Apart from that fact , it was the only scripture that told the same exact stories of Torah and bible but without any out of logic contradictions , on the contrary , It pointed out those contradictions and explained them in the most logical way .
I could never understand why GOD would need a son !! it's weakness and humanly to have one in my opinion , let alone let the creatures that he made torture and kill his Son !! never sounded logic to me , and the idea of it doesn't matter what you do in life because someone else have paid for your sins by being tortured and killed and all you have to do is believe that to be saved from hell never sounded FAIR to me.
On the other hand Islam didn't say you have a free pass to heaven cause you believed , and you can be a muslim and still go to hell !! it all depends on what you did in this life , EVERY SINGLE word you say or deed you do is written down , and in the day of judgement all those are going to be weighed before you , good on one side and evil on the other , and whatever you did decides your fate . Sounds FAIR to me.
No free passes , you're the only one paying for your deeds , however , It's Easy to repent , you do not have to confess to another human being to do that . all you have to do is ask god for forgiveness and confess your weakness and sins to him (no middlemen) you don't have to go anywhere to do that .
But Hey , does that mean i can rob someone and just pray for forgiveness and i'm done ?? The answer is NO.
God forgives what's between you and him , what involves other people is settled with other people , that means in the day of judgment/resurrection the man you robed , the woman you bullied , the wife you cheated on all are gonna come to you and take from your good deeds off of your weigh until they have taken their right back from you , if you don't have any good deeds , they will give you from their sins and you then go to hell with a weigh full of sins of others that you did wrong (EVEN IF YOU'RE MUSLIM) . Well again sounds fair to me .
The deeper i dug into that book , the more truth that i found , it tells everything about Jesus , Moses , david , Imran , virgin Mary , Noah , abraham , Isaac , Adam ,,,etc and every man god has ever sent to humanity , it has perfect explanation for our being and purpose and i could not find nor anyone till now any contradiction .
and This is why i'm a muslim and i still on the path of learning that beautiful peaceful religion.
Never be fooled with the stereotyping you hear about it , many of the muslims are the sole reason for the bad reputation about that religion by their wrongdoings and understanding of the scripture , making people think that Islam told them to do that while it's only their ignorance .