The Riddle of the Lovers' Basket

Or lastly they’re on a different planet with higher gravity.

I immediately thought that it feels much easier to carry something with the pole in the picture because the weight rests more closely to a point on the y-axis going through your center of gravity, as opposed to carrying it at the side of your body, where your arms are.

But I like your second interpretation way more!

Another possibility: how they carry the basket is different. Maybe when they were sharing the load, they could use both hands or rest some weight on their body, but when they're carrying their individual basket they can only use one hand or can't rest it on their body.

That's my guess too