[2019] Why do DD players have such a hard time understanding that it's nearly impossible for a BB to hit an enemy DD at range?

As a DD Main this VERY important. Giving the enemy DD more to think about than just me gives me a base advantage. All it takes is one of those massive shells to connect and suddenly that BB has the DD's attention.
And nothing gets a DD's player attention more than being hammered by 14 inch and bigger shell. Even an over-pen will clock a chunk of HP. It may shake him enough to make an error your DD can exploit. Your DD will appreciate the support and perhaps be bolder in spotting and screening for the BB's. Just my thoughts.