Many Christians though do see Genesis as being a "myth or Allegory", but that would be due to them accepting the "facts" of evolution as superior to biblical revelations, but Jesus Himself confirmed the historicity of Genesis account of a literal Adam and Eve
It really always comes down to what we think the Hebrew word "YOM" means. I am not taking sides here, only posting what is thought in both camps.
Young earthers believe it means a 24 hour, 7 day a week time frame.
Old earthers believe it means an "Age of time".
Source........The Theological Wordbook of the Old Testament (1980, Moody Press)
"It can denote:
1. the period of light (as contrasted with the period of darkness),
2. the period of twenty-four hours,
3. a general vague "time,"
4. a point of time,
5. a year (in the plural; I Sam 27:7; Ex 13:10, etc.)."
Source........Strong's Exhaustive Concordance of the Bible.
1. "From an unused root meaning to be hot; a day (as the warm hours), whether literal (from sunrise to sunset, or from one sunset to the next),
2. Figuratively as space of time defined by an associated term.
It is interesting to note that in 67 verses in the Old Testament, the word Yom is translated into the English word "time."
In Isaiah 30:8, it says "
Now go, write it before them in a table, and note it in a book, that it may be for the time to come for ever and ever."
In this case, Old Earth believers will argue that "Yom" here in the Scriptures is equal to "forever." How long is forever? An infinite number of years...billions upon billions upon billons of years. If Yom can equal trillions of years here, then why not billions of years in Genesis?
Again........I am just presenting the arguments and not taking sides.