Why does the LDS church believe that alcohol was forbidden, despite being common in the Bible? The Word of Wisdom prohibits members of the LDS church from drinking alcohol, but alcohol is quite common in both the Tanach (Jewish bible) and the New Testament.  Why does the LDS church believe that alcohol was acceptable to those in Biblical times, but not now? In other words, what is the reason that alcohol use was a major part of religious life in biblical times, but forbidden now to LDS church members?

(I am not a Christian, much less a Mormon, so I apologize if I have made any mistaken assumptions in my question)
Latter-Day Saints agree and understand that the use of alcohol was permitted, and in some specific instances even formally encouraged in worship rituals, in ancient Judaism and Christianity.  The revelation recorded in Section 89 of the Doctrine and Covenants explains that this is not an eternal principle, but a specific one for our day, given specifically in response to modern conditions:


  1 A Word of Wisdom, for the benefit of the council of high priests,
  assembled in Kirtland, and the church, and also the saints in Zion—
  
  2 To be sent greeting; not by commandment or constraint, but by
  revelation and the word of wisdom, showing forth the order and will of
  God in the temporal salvation of all saints in the last days—
  
  3 Given for a principle with promise, adapted to the capacity of the
  weak and the weakest of all saints, who are or can be called saints.
  
  4 Behold, verily, thus saith the Lord unto you: In consequence of
  evils and designs which do and will exist in the hearts of conspiring
  men in the last days, I have warned you, and forewarn you, by giving
  unto you this word of wisdom by revelation
  
  (emphasis added)


There are two important points given here.  First, that the Word of Wisdom was given for "the temporal salvation of [the] saints in the last days," and not generally throughout all of history, and second, that it is given "in consequence of evils and designs which do and will exist in the hearts of conspiring men in the last days."

The Word of Wisdom covers more than simply a prohibition on drinking alcohol; it covers basic principles of health and good diet, and also proscribes the use of tobacco and "hot drinks," which has been interpreted by Church leaders as meaning addictive beverages such as coffee and caffeinated teas.

Any American who was old enough during the 1990s will probably remember the Big Tobacco lawsuits.  When one considers the evidence that came out then, plus any number of less well-covered issues regarding industrial-scale food production over the past few decades, the manipulations of the "evils and designs which ... exist in the hearts of conspiring men" become plain to see, which really weren't an issue in earlier ages.