Your lack of properly packing the TV isn't UPS's problem. You decided since it was in a box designed to show features of the TV, not to ship it, that you'd assume that's proper packaging. Most TV's arrive at B&M on pallets, secured in a box type formation with other models of that manufacturer. Did you honestly take a moment to think that a 1/8th inch of cardboard was enough protection to ship your TV across the country? Some retailers choose to do this and take the loss on improper packaging because of the margin on TVs when they do get broke equates to the cost of doing buisness You rolled the dice with improper packaging and lost. UPS is going to deny your claim for that reason, and rightfully so.
A simple google search would send you to this link, to fully explain how to properly pack your 800 dollar TV. If I was shipping something that expensive, I would have taken a moment to check if I wanted to insure I was doing it correctly.
UPS: Packaging Advisor