If DS is a lengthy game like many are expecting, then it makes sense for them to get review codes out early because we're getting to a point in the year where things are packed. You've got Little Town Hero, Plants vs Zombies, WWE2K20, Modern Warfare, MediEvil, The Outer Worlds, Monkey Ball, and Luigi's Mansion 3 all coming out in the window before DS. And MediEvil, MW and TOW all come out on the same day. And for smaller sites without as many reviewers that's a lot to pack in. So giving it to people early allows them to play it without the need to rush (or at least rush as much as they would if it went out a week, or days before launch).