Why is the Bible subject to a high level of interpretation? I realise there's always a level of interpretation neccesary when reading anything, but the level of interpretation needed to understand the Bible is very high when compared to everyday reading - some people spend their entire lives trying to understand what it means.
Example
If a friend says to me:

I'm going to the shop, I will be back before 1PM.

I don't have a reason to interpret this statement as meaning 1PM tomorrow, or 1PM next week.
We could compare this to Luke 21:32:

Assuredly, I say to you, this generation will by no means pass away
till all things take place

This to me means that all the prophecies described in the bible would happen while the generation that Jesus spoke to was still alive.
However it's often interpreted to mean something entirely different. Here is one Christian interpretation:

(This refers) to a future generation that sees the events He spoke of
prophetically.

Note: I'm not asking specifically about this interpretation it's just an example - I'm asking in general why it is subject to a high level of interpretation.

Is it because the Bible was written in another language, and we can't
assume it has been translated properly?
Is it because the Bible states
that it's not always to be taken literally?
Something else?
The Bible is subject to several different types of interpretation and criticism. This is for various reasons:


It was originally written in languages that are no longer spoken. The ancient Greek and Hebrew that it was written in are similar but dramatically different than the current forms of those languages (languages morph and change over time).
Translation from one language into another is not a lossless conversion process. You can lose some of the meaning and significance in the translation from the source material. You can also introduce noise into the new copy through lingual nuance. This is why so many different English translations of the Bible exist; reading several translations will often give a clearer picture, but sometimes you just have to go back to the original language.
It was written for and by ancient cultures that we share very little cultural reference with.
It was written over a great deal of time by a variety of people in a variety of places on a changing cultural landscape.
It's a piece of historical literature and thus subject to the same interpretation and criticism as all historical literature is subject to. Pages and volumes of ink has been spilled on Chaucer and Shakespeare, in more recent times, and Plato, Aristotle and Josephus in more ancient ones.
It is considered to be the word of God. If God spoke it then it should be examined carefully to see what it says.
Finally, it is considered to be "living" meaning that it is constantly applicable to our daily lives, even though it was written ages ago. To emphasize this Hebrews 4:12-13(NIV) 



  12 For the word of God is alive and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart. 13 Nothing in all creation is hidden from God’s sight. Everything is uncovered and laid bare before the eyes of him to whom we must give account.