Why Is It Better to Put I-E-R at the End of the Adjective?

If adjectives ending in Y, we usually, in good, correct English, put I-E-R at the end. For example, expensive has three syllables - it's not correct to say expensive. So even though we say cheaper, we say more expensive than. Can you think of an example, Besser? Well, grammar books are more expensive than this podcast. And another example, snowboarding is more dangerous than podcasting. Here's a question for you, Reza: Do you think science fiction is more interesting than history? No, much less interesting.