Think about it this way: collecting taxes from states was a two-party relationship. The states were compelled to pay in this transaction, but it's still two parties on opposite sides of the table, and their are other topics to negotiate later. If the federal government were to play an obvious game of taking money and then giving it back with conditions, then states would have exerted their power in other transactions. For instance, with senators who were chosen by the state legislature (the same body paying the taxes). Additionally, the state is a stronger entity to fight back against this kind of abuse than an individual citizen.
Now, let's change the picture to directly-elected senators and direct taxation. Now, the money is collected directly from the citizens first, and then the government's relationship with the state is entirely different. Now, the state and the federal government are cooperating, and the sucker is the one not in the room: the citizen whose money is being passed around. The state just becomes a node in a hierarchy, rather than a formidable agent with its own powers and responsibilities.
It's actually very similar to negotiations with a public employees' union. The government and the union are "negotiating", but they are really on the same side of the table. The sucker is the citizen who's paying for it all, but isn't even in the room.