So why is 1 Alternative Account allowed for Deposit beside the main of course? Isn't this a bit silly? Some Sellers are buying big amounts of Steam Gifts per hour and Selling it on Dispenser isn't that a time waster that we must send the Gifts to our main or 1 alt deposit account and then send again to the Bot ? It's a big time waster but I really don't get why is this done like this.

Because there are people having 10+ deposit account and it was just wrong. We had over 450 deposit account out of ~100 VIP.

The buyers can never tell who exactly bought the gifts. Because some of the deposit accounts are actually different people rather than the owner's alts. People can still share with one other person even with this change, but the damage is controllable.