No way to go slowly as steep as that is and then get to the top. Have to question the skill level of people doing this knowing they're likely going to damage their bike trying. Not watching it twice but it seems like it's just a few going again and again..
I've done a little hillclimbing in the 1980's on my big bore 2 stroke bikes. It looks easy, right up until you try it. The idea that something slow can crawl up a hill with loose traction is incorrect. They just dig in and come to a stop.
HP is king.
On sandy climbs, the spinning tires create thrust by displacing the sand. The higher the HP, the higher the thrust, and the more likely the bike will make it to the top.
I used to go to the Widowmaker hillclimb. Horsepower, a paddle tire often with chains, and an extended swingarm was just about the only way to have a chance. Most of those who were successful, burned Nitromethane.
Going slow wouldn't get you very far. A 4x4 ATV without a seriously extended swingarm, would just roll over backwards.