I can think of several reasons right off the bat
- Best vs 2nd best is a subjective call and often changes once they hit the nfl
- trading down lets you acquire more picks. Often 2 good players can have a stronger impact 1 really good player .. not always though
- Your determination of 1st vs 2nd might be different than the person you are trading with
- You always have positions of need
I don't think you should always have positions of need. We really didn't have any going into 2006 which is why it was a perfect time to take Leinart, or 2009 when we had a solid veteran team and were able to attempt to take mostly young guys to step in 1,2,3 years down the road.
Heck, the Cards really haven't had any positions of need, other than HC, since 2005 except for 2007 and that was only because they didn't extend LD.
Like I said in another thread its not like we've had Fred Wakefield playing OT or Bryan Gilmore as our #1 WR.
That's why this season is so frustrating. We've been drafting for upgrades and buying futures contracts for 5 years and it hasn't panned out.