Why is it that Active has to go in front of a promotion board and Reserves don't?

You will drive yourself insane doing the "How Come" between Reserves or NG and active duty..
Forinstance, why does an Active Duty SM who wishes to be an Infantry Sergeant Team leader have to go through 14 weeks of OUST, be selected for promotion several times, train at the individual, team, squad level for somewhere north of at least a year to be selected and promoted to Sergeant E-5, 11B.. But the reserves can build an Infantry Sergeant in two weeks having had no previous Infantry training of any type?
How Come........ad nauseum.. end of the day, it's as simple as those that control the play book, wrote the rules that say they can.

I think it's more so a tradition than anything else. Should be like the Air Force and just take a test

You asked a great question and it was answered by a few of the other comments listed. I went from being Active Duty to Reserves this past March. I got promoted a year before I went to the Reserves. It seems that you are nervous about going to the promotion board, if this is the case then you can ease that by doing practice boards, soldier of the month boards ect. The fact still remains that to get the promotional status you have to show to the senior level leadership that you can show them that you have the qualities to lead other soldiers, to handle not only your own situations but also their situations if need be. Anyone can give "orders" or directions but enforcing the standards and being the one that soldiers look to is different. The board can be hard and nerve wrecking but if you can't handle that pressure how can you handle the pressure of leading soldiers both in garrison and in combat? Your leadership sees potential in you if they are recommending you to the board and presenting you to the board. See what they see and always make decisions based on what is both morally and ethically right, as long as you follow that you will do fine. Hope this helps and best of luck.