What the hell?

Okay, there are 10 witnesses. If he doesn't distribute his stake into two accounts, each of the witnesses he votes will get a x sized vote.

Peter1 -> x
Peter2 -> x
Peter3 -> x
Peter4 -> x
Peter5 -> x
Peter6 -> x
Peter7 -> x
Peter8 -> x
Peter9 -> x
Peter10 -> x

If he splits his stake into two accounts, each of the witnesses will get a x/2 sized vote.

Peter1 -> x/2
Peter2 -> x/2
Peter3 -> x/2
Peter4 -> x/2
Peter5 -> x/2
Peter6 -> x /2
Peter7 -> x/2
Peter8 -> x/2
Peter9 -> x/2
Peter10 -> x/2
Peter11 -> x/2
Peter12 -> x/2
Peter13 -> x/2
Peter14 -> x/2
Peter15 -> x/2
Peter16 -> x /2
Peter17 -> x/2
Peter18 -> x/2
Peter19 -> x/2
Peter20 -> x/2

This gives each of his vote only half the influence.

Yes, the total quantity of stake voting is the same, the influence is smaller. Since he can't push so many people into the top ranks.