You've misunderstood. Practically speaking, the UK needs to buy shit, the US needs to sell shit. UK has effectively blocked out 1/3 of the world (Europe) from a trade deal because we'd never get one as good as the current free trade agreement with the EU. Our politicians won't be stupid enough to say "we've left the EU, but have made a worse deal with Europe than we had before". Similarly EU won't make a deal with the UK which disallows freedom of movement and other "core" EU values, so any deal made would either require circumstances similar to pre-brexit EU to happen, or would just flat out be a worse deal.
Distance really isn't much of an issue at scale, when your cheap stuff comes from China - - edit - to clarify, the point i'm trying to make is that it really doesn't cost much to ship stuff halfway around the world, especially en masse. -, or meat from New Zealand, this isn't much of an argument. This would be a purely US beneficial deal, the UK wouldn't really be bringing anything into the US, other than maybe finance services, specialist products or (i guess) softer products like educational visas?
There's quite a big controversy over here at the moment about the possibility of a US trade deal. We are being told that for it to happen we would have to accept terms like chlorinated chicken/steroid injected beef, and then agree to other things like labeling the origin of the product (so you would never really know if you were eating US or UK products). There's a whole other host of subtleties which would degrade the UK whilst being beneficial to the US, just do a bit of googling about the proposed deals.