Short Answer: Because Muslim are supposed to live their lives by the Qur'an and Hadith.
Long Answer: Lets look at the actual pertinent scripture. I will be answering this taking the Qur'an at face value to provide a more genuine answer, so please pardon me if that offends your sensibilities. Ok, so Alcohol is explicitly forbidden in the Qur'an in these 3 verses:
"They ask you about wine and gambling. Say, "In them is great sin and [yet, some] benefit for people. But their sin is greater than their benefit." And they ask you what they should spend. Say, "The excess [beyond needs]." Thus Allah makes clear to you the verses [of revelation] that you might give thought.
"O you who have believed, do not approach prayer while you are intoxicated until you know what you are saying or in a state of janabah, except those passing through [a place of prayer], until you have washed [your whole body]. And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and find no water, then seek clean earth and wipe over your faces and your hands [with it]. Indeed, Allah is ever Pardoning and Forgiving."
"O you who have believed, indeed, intoxicants, gambling, [sacrificing on] stone alters [to other than Allah ], and divining arrows are but defilement from the work of Satan, so avoid it that you may be successful."
So, as you can see, the stance is pretty clear. In a chronological sense, these chapters were revealed in the following order: Nisa/Baqarah/Maidah. While the Qur'an is not assembled chronologically, it is important to look at these verses in such an order to better address this question.
First in Nisa, what God is saying is that believers should not approach prayer in a state of intoxication or Janabah (sexual impurity). Now, by mentioning these together, we can infer a parallel between the two: Where after ejaculation/intercourse a person is in a state of physical impurity, intoxication puts a person in a state of mental impurity. I draw this inference from these words:
until you know what you are saying
By including that as the qualifier, it can be understood that God has deemed that an intoxicated person in fact does not know what they are saying. Therefore, if he/she cannot communicate with their immediate situation, how could he/she possibly communicate with God? Both of these conditions are strong enough that it is advised a person not approach prayer until the impurity has passed. So from here, we draw that intoxication renders a human in a mentally impure state as far as God is concerned. Impure enough that a person not approach God while in that state.
The next revealed surah was Baqarah. Here, we can see that the tone towards acohol has clearly gotten harsher. In Nisa, there was a seemingly implied 'acceptance' of intoxication, because instead of outright forbidding it God simply says do not approach prayer while intoxicated; implying that people will drink in the first place. In Baqarah, we start seeing explicit condemnation of drinking. In contrast to making provisions for the drunken person, God is outright saying intoxication and gambling bring about more harm than good. Pretty straightforward.
Finally, we get to the latter surah: Maidah. Here we can see the tone has clearly gotten harsher still. In this Surah, God ups the condemnation of intoxicants from a harmful indulgence to the outright handiwork of the Devil himself. Because Satan only seeks to lead man astray and towards ruin, "Avoid it [intoxicants/gambling/divinaton] that you may be successful"
SO, here is what we have drawn from these 3 verses of the Quran:
Intoxication renders a person in a state of impurity severe enough that prayer is discouraged in such a state
There lies in alcohol more harm than good
Alcohol is the handiwork of the Devil, in that the consumption of it distances one from God (Nisa), Is harmful for the human (Baqarah), and that consumption of alcohol often leads to indulging more of the Devil's whispers.
It is from these assumptions and beliefs and for these reasons that Muslims are prohibited from consuming alcohol. Not just Alcohol, but rather any intoxicant. The other thing Muslims are supposed to live by is the Hadith of the Prophet. In that regard, there are many authenticated Hadith on Alcohol and Intoxicants. One such example which goes a long way in establishing what is an intoxicant, and therefore Haraam, is this one:
Jabir (may Allah be pleased with him) narrated that the Messenger of Allah (Peace and blessings be upon him) said; "Whatever intoxicates in a greater quantity is also unlawful in its smaller quantity." (Tirmidhi, Abu Dawood and Ibn Majah)
The point being, as opposed to the conventional Christian view on the matter, a single beer is forbidden even if it's not a sufficient amount to induce inebriation.
So, that is why Muslims are not allowed to drink alcohol, from the religious perspective. Im sorry if thats not a 'historical' answer, but the reason is quite literally that intoxicants are forbidden in the Qur'an, so I have elaborated on what the Qur'an has to say on the matter. I hope thats a sufficient answer.