Many words in the English language have strange origin stories, but those words created by simply spelling a pre-existing word backwards have a very straightforward reason for existing- wordplay.
The Brits turned Yob into a cool slang term for a lad who's up to no good, a well flipped word that rolls off the tongue and easily gets its meaning across without explanation.
And when Dylan Thomas set his play Under Milk Wood in a Welsh town called Llareggub ("bugger all" spelled backwards)- now that was bloody brilliant!
It's not hard to conjure up an explanation for why the sorcerer in Fantasia is named Yensid- the character was modeled after Disney and symbolizes his "magical" imagination.
And if you're long in the tooth like Yensid you may need help with irregularity, so those who wanted to hear nature's call on a daily basis would take Serutan, nature's way to “provide peristaltic stimulation.”
See 9 Words Created by Spelling Other Words Backwards at mental_floss