First and foremost, it's because they aren't lasers. I know they're called “turbolasers”, but official lore marks them as something other than pure light (some undefined “energy” enhanced by Tibanna Gas). read more
As to why the First Order would choose to arc the shots, they may have wanted to target the bridge (at the front of the ship) or the top shields (perhaps they’re weaker). That’s all an in-universe explanation, though. read more