Simple, the price is much cheaper, and the iPhone 8 does not have many new features over the 7.
If you want wireless charging, sure get the 8, but other then that and a slightly improved camera or CPU, the 7 is a better buy.
How much cheaper is a 7 over an 8? $50? Anyone that needs more than 32 gigs is going to be forced to spend $650 for the 128 gig even if a 64 gig would've been plenty; sure storage is double for 50 bucks less but it's classic Apple upselling you and most people buying a 7 could probably get by with a non-existent 64 gigs, but are forced into a 128 gig model and only saving $50 over the 8. Seems like saving $50 on the front end only costs you on the backend when support is dropped for the 7 a year earlier. Or if you sell it before support is dropped, it's correspondingly worth less on the back end since you paid less up front. At that point you may as well just get the 8 since you aren't really spending much more keeping a 7 or an 8 for two years and then selling it. Pay more up front, get more on the back end which basically makes it a wash to buy the 7 or the 8.
Personally I just cant get on board with still shelling out $700 with tax for a phone that's been out for 15 months already. With Apple, I feel it's much better to get the newest, and get it when it's a fresh release to maximize your dollars on the purchase (e.g. no point in buying a Macbook Pro that was released 9 months ago for the same price as 9 months prior).
The iPhone 8 is not much more expensive but is much more capable with the bionic processor technology, graphics performance, huge camera improvements, better display, more battery life, refined design, etc.
So cheap out if you want. But don't moan when your iPhone 7 slows down next year as Apple targets iOS 12 towards taking advantage of all this awesome new hardware in the latest and greatest iPhones. You really want to get on board the bionic processor train ASAP.
I'm not as enthusiastic about the processor as you, but yes, the 8 will outlast the 7.
Honestly I've always scratched my head wondering why anyone bought a 7, between the 6/6S/7/8, the 7 was the lamest upgrade. The 8 is a really, really, really nice upgrade over a 7, if for nothing else than the glass body, let alone processor, camera, GPU, wireless charging (not a gimmick, use it every single night), etc. etc. The 8 is one hell of a phone and will have longevity like the iPad 4.
