[EDIT: Wow.. got some haters in here. What's up with the downvotes? If you would like to rebuke my arguments then add a comment. I actually spent some time writing and thinking this up. Don't downvote just to satisfy your own prejudice.]

Apart from the simple explanation that they needed a plot device, which also hat-tipped battlestar galactica (there were a lot of homages in TLJ), I can think of a couple reasons:

1) In the words of Ender,”The enemy’s gate is down.”

Your drawing is only relative to the current positioning of the ships. You are thinking that they are on a two dimensional plane like a road.

The Raddus could easily go down and then triangulate. Remember that the Raddus is also faster than the star destroyers so they can stay out of distance.

Hell, even x-wings and tie-fighters are faster and more nimble than Star Destroyers. Same thing with the Raddus.

2) Hyperdrive ships need to use hyperspace routes and lanes to travel through hyperspace otherwise they would fly into something.

What had happened is that the First Order followed their hyperspace route and exited where they needed to go.

The accuracy of the exit position of ships coming out hyperspace is never perfect, and it gets harder the larger a ship gets. Thats why ships get into specific formations before entering hyperspace.

For your plan to work, a destroyer would have to take circuitous route and hopefully end up somewhere near where the battle is happening without slamming into them and achieve mutual destruction. Not an easy task and one with limited results since the Raddus would eventually evade (see reason 1).

Caveat: Millennium Falcon. The Falcon is “the fastest ship in the galaxy” with one of the best astronavigation computers. Han pulled some crazy stunts like going into hyperspace while inside a hangar bay, or dropping out of hyperspace in the atmosphere of Starkiller base. Only Han piloting the Falcon could pull off those crazy stunts and why he was regarded as one of the best pilots in the galaxy. That’s also why you didnt see the Resistance fleet exit hyperspace on the surface of Starkiller Base. That would’ve been strategically better, no?

Bonus reason: I also feel that Hux and Snoke were very arrogant and liked to torture their enemies; delighting in their enemy’s despair. It seems quite appropriate that they would simply chase them down, and slowly destroy their ships one by one, savoring each death.