In Japan the most common size of motorcycle is 400cc and smaller and the reason for this is entirely practical.
Part of the Japanese motorcycle test requires you to lay your bike on its side on the ground and then to pick it up on your own. The Japanese not being the largest of people and there being nothing heavier than a motor bike on its side means that they choose smaller motorcycles.
I think the same rule should be applied to luggage on public transport.
If you cannot pick up your own luggage or if it weighs more than you or a small horse in some cases, you should not be allowed on public transport.
I am fed up with being stuck behind tourists with huge cases as they struggle to move on and off trains and up stairs at stations.
Get a taxi or travel lighter please.