Some do. They always rely on faith when they can't understand science.
Show us anywhere at all that creationists are claiming this.
And the mistake you are making, is assuming that people who believe in God do not "understand" science. They understand it plenty well. Well enough to realize that evolution doesn't have any chance what-so-ever of being the explanation for living things.
But, if you have enought "faith" you can continue to believe it :-)