Unfortunately, the real answer has nothing to do with logic, Imperial tactics or the Death Star's capabilities.
The Death Star shot wide so that we could watch the explosion roll in over the horizon as Jyn and Cassian held each other on the beach, knowing that they were about to die. They were going to die heroes, and we got to watch it happen - slowly.
It was incredibly emotional. Why? Because you watched the explosion coming right at them - and so did they.
Thousands of people died when the Death Star blew up Jedha City. Did you feel for them? Nope. Because you didn't see them.
Billions people died on Alderaan. Meh. It was just a planet on a monitor.
Over a million people were killed on Death Star 1. No one cared. Same with Death Star 2.
This was the first time we saw a Death Star explosion that was not instant death, and it was dramatic - but it made no sense.
They justified it by having the Death Star's beam destroy the dish and Krennic. But, any TIE Striker, TIE Fighter of AT-ACT could have done that earlier.
Why would Tarkin destroy all Imperial architectural plans (no backups) and the Scarif base, just to kill 30 rebels and a guy he is mad at? I don't think that would go over well with the Emperor. Scarif is where the Empire built its war machine, so they say.
Tarkin only uses the Death Star, and aims wide, to create a movie moment.
Bear in mind this is a franchise where the Force does not awaken. Details like this will drive you mad unless you remind yourself that it was only a movie.
Also, you might as well ask why the Empire would build an archive to store TAPES (or hard drives) of architectural plans - and design it like a tower vs. a regular building with normal shelves - when we know they have an Imperial computer network?! Again, this was just designed for a cool action scene that was straight out of a video game.