I wish someone could explain to me why we can not present both theories, all ideas ~and let the children decide for themselves.
Which two theories are you referring to? Why do you pick those two as the competing creation stories to present to children? (or why did you exclude the other 10,000 creation stories?)
There is one scientific theory of evolution, and there are thousands of creation stories that more or less disagree both with each other and the scientific theory. Present one of the religious creation stories, present them all, I say.
"Intelligent design" or "creation science" or whatever you wish to call it is not a "theory" as scientists use the term. What you are asking is a sort of affirmative action for your preferred creation story.
There are two reasons. First, children are not competent to evaluate such material. That is the province of experienced scientists. Schools (pre-university level) exist to present students with the best available information.
Second, the overwhelming opinion of scientists in firm agreement that there is no scientific theory other than evolution which explains the material in question. Specifically, Genesis is not a scientific theory, and ID is a wild conjecture with no data, no research, no testable hypotheses, and no scientific (peer-reviewed) literature.
Or--they're attempting to chip off a few votes from the GOP, as the religious are a reliable and helpful constituency. It wouldn't take much in a few vulnerable elections to turn one or more Houses--Senate or Reps--to the minority party.
Or--there is a libertarian/ACLU mentality which cannot bear to have the religious have any say in public life, no matter how they've earned it in grassroots mobilization and voter services.
Could be some of the above.