It has everything to do with limiting God. The first limitation you place on him is taking away his ability to speak in anything except a linear, literal, chronological manner. He’s not allowed to use metaphor or symbol, at least not until you get to John chapter 6.
The problem with that theory is that in order to use a metaphor, it has to shed light on what it is being compared to...
And the best you guys can do is to say that, 'it doesn't mean what it says, but we have no idea to what it is alluding to'...
It is then no longer a metaphor...
A metaphor is used to emphasize the qualities of something by saying they are like another.
Metaphor - Definition and More from the Free Merriam-Webster ...
a figure of speech in which a word or phrase literally denoting one kind of object or idea is used in place of another to suggest a likeness or analogy ...
If you don't know what the likeness is, the term metaphor has failed...
You may believe Genesis is a metaphor for something else but if you don't know the something else, you need to find a different theory...
There is no reason to suggest God uses metaphors in Genesis Creation when you can't get a clear picture of what He is saying by using the metaphor...That's the reason for the metaphor...
The problem lies not in what is being said in Genesis because it's pretty clear...The problem is in believing it...
And then there's the motive...What reason does one have NOT to believe what God said literally???
And does God speak in metaphors??? Sure He does...Look at Song of Solomon if you want metaphors...But again, there you will get a picture of what the metaphors mean...Completely unlike your suggestion of metaphors in the Creation story of Genesis...