Because what Cheveldayoff is looking for is quite unrealistic. There just aren't teams looking to trade a young LHD for a righty at the moment (see: Buffalo and Anaheim). Chevy's going to have to take a more seasoned veteran top-4 LHD (and a capable player, which Jack Johnson is) with picks/prospects to make it work.
You could point out that Ryan Murray would get the job done, but it would take a significant add for the Blue Jackets to consider. Murray, at the moment, is their best defender. Much like what viqsi pointed out, moving Murray for Trouba would put us in the same position as the Jets. So it would take a hefty haul for a Murray for Trouba+ swap.
Contrary to popular belief, Jack Johnson is a very solid top-4 defender when not thrust onto the top pairing with an incapable partner. That's why Jack Johnson + one of our prospects not named Dubois/Bjorkstrand/Werenski is a good alternative for WPG to consider.