the lead single didn't hit with people.
Every first single Em had, forced or not, hit big
My Name Is, The Real Slim Shady, Without Me, Lose Yourself, Just Lose It, Crack A Bottle, Not Afraid, Berzerk
all those songs were big hits
Walk On Water? not so much.
On top of that, people expected the hit single to be something forced but then the album would have heat. Word of mouth in 2017 spreads much faster than it used to, and it got around to people that this album was not that good. This album won't have legs going forward.
Jigga did less first week than Em but at least Jigga had that built in deal with Sprint and critical acclaim. Em before you know it will sell less than TWO Post Malone albums