Why can't we make an iphone backup to a lightning jump drive large enough?

not sure what a jump drive is but if it's anything like an usb stick or external hd using usb then you can suggest it to them using their feedback channel (though ios devices can't provide enough power out of it's connector to power external harddrives that rely on power from the host)

Product Feedback - Apple

Probably because it's a very bad idea to use a jump/thumb drive for backup or long term storage.

A thumb drive degrades slightly every time you write to it. Granted it may take hundreds or even thousands of write cycles to damage it but why chance it.

An SSD drive uses similar technology, however they have a lot of redundancy built in to allow for damaged memory.

Rudegar wrote:

not sure what a jump drive is but if it's anything like an usb stick or external hd using usb then you can suggest it to them using their feedback channel (though ios devices can't provide enough power out of it's connector to power external harddrives that rely on power from the host)

Product Feedback - Apple

"Jump Drive" is just another name for "Flash Drive" – possibly a trademarked marketing name of a particular brand or brand line.

iphone will not let one draw any power from it's port, if the ssd drive would not be powerd by it's own ac source it would never be able to run

as stated

This is a user helping users with tech questions, we are not apple and apple do not read your posts here

If you wish to reach out to apple then try  Get Support (apple.com), or 

Contact - Official Apple Support

Or provide them with feedback Product Feedback - Apple

It is up to you to suggest new features that you would like to see incorporated for the iPhone.

Feedback - iPhoneAppleApple › feedback › iphone

For what it's worth......users have been suggesting this type of feature or option for years.

What do you mean how long? Apple has not announced any such feature.