What is the purpose of landing on the rear tire?
Landing on the rear wheel is a safe bet when you are not sure about the landing zone.

For example a small tree root would be catastrophic if you are landing with both wheel. What happens is that since the downwards force from the fall is applied to both wheels, it is much harder to roll over the obstacle. If the front wheel cannot roll over, you basically flipped.

But it is ok for the rear wheel to struggle to roll over an obstacle, as you can always drop the front wheel, balance the weight and roll easily over.
After the initial landing, there is always a bounce-back where all the tyre and spokes compression/tension is released.

It is better not to lose traction on the front wheel upon landing and thus landing on both wheel is also not a good idea.


What actually happens is 1) they are not exactly landing on rear wheel, it is an initial touch-down to reduce the falling momentum, 2) the body still continue to fall but decelerates thanks to the rear, 3) critical step to distribute the remaining falling momentum onto two wheels: too much on rear you will break something (minor) or even worse it will pump all your weight to the front wheel (see video at 34:54), too much on the front you will either flip or lose traction as previously discussed.

Having said all the above, what is important, perhaps a lot more important than whether you land on rear first or front first or both at the same time, is that you can extend the duration of impact as much as possible. This reduce the bounce-back as discussed in 2. Landing rear first is one way to prolong the impact and is also safer than landing front first.