Some users have tens of thousands of accounts. How much does limiting the number of witness votes they can cast per account affect them? Sock puppets will get around any limitation on witness votes per account, to greater or lesser degree depending on how limited witness votes are.

If you reduce the number of witness votes an account can cast to one, @justinsunsteemit can spread his stake to 20 accounts and replace the consensus witnesses at will.

Frankly, equity really demands 1 steem = 1 witness vote, and you can see how the present system is inequitable and centralizes governance now if you read this.