How do you get over a fallen tree? How do you get over a 5 foot wall in an urban environment? It needs to be carried by the men on the ground to truly be versatile.
Same thing with a mule, robo-mule or a self propelled vehicle.
Wait, I can detach the bags from a bike/trolley and throw them over the 2m wall with a help of a comrade/short rope. Then goes the 15kg bike or or the trolley.
And unless we are talking about the jungle/fallen trees/mountain warfare etc., where probably anything non-human can not be used effectively, you will be faster and less tired reaching the destination.
Last but not least: simple trolley is quite cheap, way cheaper than the load it can carry. You can throw it away when the going gets tough.