This will be happening for quite a few reasons:
1. The iPhone 14 and 14 Plus are basically the same as the 13 line up, there is likely good deals now on those devices so people will likely opt for them over 14’s as they will get a similar all round device for the same money if not cheaper.
2. Pre-orders are normally flooded with tech enthusiasts not your general consumers, meaning the Pro line up is what is likely to sell quicker during pre-orders.
3. The main new device in the standard 14 line up is the 14 Plus which won’t actually ship until 7th October… which is quite a bit away yet.
4. The current economic climate is discouraging people making large purchases or taking out new carrier contracts,
5. In some respects this is what Apple want, as the pro line up likely has a much higher mark up than the standard 14 line up, that’s why there is a severe lack of innovation with the standard 14’s, it’s a perfect business model for upselling, Apple want you to go with their Pro line up over the standard line up.
I think in the long term overall though the iPhone 14 Plus will end up being the best seller, the Pro Max second, Pro third and the standard 14 being the worst seller of them all.