They have done. It's called Doctor Who. Seriously, look up the impact it's been having on kids for decades, now.

Didn't Ron L. Hubbard do that?

There is a wonderful and growing wealth of fantasy fiction available, much of which is very secular in origin, think of Philip Pullman and others. But it is true that in the arts and heritage generally the secular movements are far behind the churches and temples. However, that is only because they have a multi-thousand year head start so we will catch up in the end. So in the mean time, get writing, painting, compose music, and design buildings to express the glories of reason, skeptic thinking and science, it does not have to be great art, everyones contribution is worth while, if only because it adds to the growing movement, and you may even get lucky, like the humble country flute player who inspired Mozart, to be the trigger for something bigger.

I reckon you heard of my uncles stories to my children... I can;t wait to one day tell new stories to my future grandchildren... Ha, he, ha.