I had a big post lined up about exactly how big a miss Silva and Neymar would be and why but the match was kicking off so I left it. Now I wish I hadn't because the effect is pretty much what I predicted, albeit not quite this dramatically.
Neither Dante nor Luiz are defensive leaders and both are prone to following the ball. Silva is the one who organises the defence, tightens up space and makes sure the fullbacks get back and in position. Even ignoring how prone to silly mistakes both Dante and Luiz are, without Silva there's no organisation... which is why Germany were so rampant down the flanks.
Without Neymar there's little creativity in Brazil's attack. There central midfield pairing (and pretty much all of their centre mid options) are hard working, hard running box-to-box players but they offer little creatively. The likes of Hulk and Bernard are powerful/fast (delete as appropriate) runners but have limited end product while Fred is well... Fred. On paper only Oscar offers any creativity, but he's looked jaded for a while and has been underwhelming all tournament.
Because the instinct of pretty much every one of those players is to run with the ball they're easy to predict and defend against. More, they like to get forward which means against a pressing team the defence isn't left with many options. Luiz firing off long balls may have been a tactical decision but I suspect that it's more likely it was because he didn't have any options to take the ball nearer. Neymar avoids that. If a team doesn't mark him then he'll hold the ball, drive and look for the pass. If they do mark him closely then there's space that those runners can actually exploit.
On a side note, it's not as if Germany have actually been stunning... Özil in particular has been utterly awful.