Why are running backs first?

I'm not really sure. I had 1st pick and took LT. I thought about taking Brady just because last year his numbers were out of this world and QB's get a lot more points but now I'm glad I didn't take him. I drafted a lot of WR's so I'd have both a lot of depth and I could make trades with them if I wanted to because everyone is loaded with 20 RB's and then they realized their screwed halfway through the season. You really have to draft smart and its personal preference on what position players you take first.