Why don't the career districts volunteer?

Now I get the fact that in order to keep the reapings fair you guys need to randomly pick who goes into the games but why don't you have the tributes for districts 1, 2, and 4 volunteer. I was thinking that you still randomly pick a tribute from those districts but instead you PM the creator of that tribute and let them chose if their character is reaped or volunteers and if I confused any of you please just ask me to explain a my idea in a little more detail.