I don't know man, they wouldn't want to risk alienating any potential sales by out-pricing the average consumer. It's cheaper for them to make two options this year, as the market will adjust to the new pricing of the iPhone X, which is already underway. The new price for an iPhone will be $999.99 USD +moving forward since that is the price the market is willing to pay.Umm, right. Or they could have done that even more effectively by not even releasing an iPhone 8. And watch this space for the iPhone 9 (8S) to slot in neatly behind the X before they get rid of the old line.
You also have to remember that in the US at least, most people pay for their phones through monthly installments. For this reason, people are willing to pay for the more expensive phone since there isn't as much of an upfront cost.