Because most of what's written is very clear and in no need of different interpretations. When people start talking about interpretations they are usually (not always) trying to pervert a clear teaching of the bible.

If it's clear why did it take you 20 years to grasp it?

Along side the clear doctrines are deeper things to grasp and correlations. The bible is simple enough for a 5th grader to understand and deep enough to study your whole life. The things that are brought up by atheists for the most part are very easily understood, but they don't want to understand them and they don't actually look for context.

Six days work shall be done, but on the seventh day you shall have a Sabbath of solemn rest, holy to the Lord. Whoever does any work on it shall be put to death. No interpretation?

The work week and sabbath as set forth in the mosaic law, is done as a symbol of remembrance for God's creative works. Just like communion is a symbol of Jesus giving his body and blood for us on the cross. It's not an exact representation of the original, it's a symbol. And Genesis chapter 1 is written poetically. It conveys literal truth, but in a way that's easy for anyone to understand. Contrast it with the book of numbers, both written by Moses but in very different styles. Edit: after reading your question again, are you asking about the death penalty? If so, breaking the sabbath was a capitol offense in the theocracy of ancient Israel. No interpretation needed.