1. Most of the officers involved were killed, so their reports do not exist.
2. The Emmitsburg Road was about 250-350 yards from the Union lines, making the attempt very difficult.
3. I don't believe from the Confederate positions from the starting point of the attack, had a good view of that part of the field, and therefore, and may not have realize the fence was there.
4. The attack did not go as planned. Instead of one contiguous line advancing perpendicularly towards the road and fence or due east towards the Union lines, the main attack was to swing like a right hook; advancing first to the SE and before getting into small arms range, swing to the NE and roll up the Union lines with an oblique advance. This planned advance would make the attacking lines in parallel with the Emmitsburg Road and fence, so tearing it down may not have been seen as a necessary.
This is all of course extremely debatable, since so little evidence exist. Pickett's report was destroyed by higher ups due to its inflamable content.