Why has no one made an iPhone case that adds extra memory?

Like this is literally a million dollar idea is it not? Just make the case cheaper than the extra $100 they charge you to go from one size to the next and you've got a protective iPhone case and you fix the huge problem of not having enough memory for the iPhone with no possibility of a SD Card. I remember there was a startup company that had an attempt at this and they said it really worked, but they didn't have the funds and ended up having to disband and the idea and model was lost, and this was like 3 years ago so in our modern time we should be able to get an extra 128GB into the back of an iPhone case with not much physical size added to the bulk of the phone compared to the popular LifeProof case.

So why hasn't it been done? I figured all the big case companies like Encipio and LifeProof and CandyShell would have all tried to do this a long time ago? Considering a 128GB flash drive costs suppliers less than $30, you could spend $10 on materials and sell it for a minimum of like $60 and you'd make bank. You could offer a waterproof version thats the same as LifeProof except its got 128GB of extra storage space and charge the same amount for it. Since it would need power, you could make it slightly thicker and make it a storage space and an external battery so that the battery can power the use of the extra storage space as well as recharge your phone when you need it to.

I'm going to design it as my final project for my drafting/CAD class so these ideas are mine!

Apple has made that technically infeasible.

This can be done with a number of Android devices with memory ports, but I see no point of incorporating memory that actually fits inside of the phone to be in a cover.

Supplemental batteries in a cover is a more sensible idea, and has been done.

You can put whatever you like in the case, but the phone is not able to use it…

Iphones (or ipads etc.) simply do not have any facility to use external memory.

Also not that the 'Lightning' port now used on i-devices is a complex data bus and anything that connects to that must be approved and licenced by Apple, or the device will refuse to communicate with it…

The only thing you can do relatively easily (without complex electronics to interface with the data bus) is connect power.

[Electronics designer & programmer for 40 years].