So you know that the cart lets you carry more stuff but it also seems to limit what places you can go to. There is other way to carry more…
Guide to Carry More Stuff
Adding pack mules gives half the carry capacity of carts (500 compared to 1000). But they actually increase the number of places you can go instead of hinder it.
They can be recruited at the first city in the stable to right of it after a quest.
And a second one to the west of the first city after crossing the forest go north along the hill. You will need stables and a watering trough to recruit them.