Well they did put SafeWater™ under most of the log. That rock under the left side of Reb's side of the log is sort of just reason for rebs to hurry at least halfway across the log before they hunker down and BlockMeme™ like Soldier was doing in that video.
(I'm glad it sounds like block FP drains are being buffed next balance patch.)
Also, heading across the log is something of a calculated risk, since not only does it give you a faster route and a flank on any direct bridge defence, it also doesn't set off the alarms for the Merc team the way the bridge does.
Aside: The "give me some ammo" spam in that video reminds me that I once saw a guy named Smamo who spammed "Give me smamo!", "GIVE ME SMAMO," and "Somebody give me smamo over here." It was a really good joke.