Most cities are, in fact, on a river.
Electricity is also a factor. In the 19th century, you had a lot of industries being built along rivers so they could run on water power. This drove up the price of riverfront property.
The electricity made it possible to operate a factory anywhere. Industries quickly moved to cheaper locations. The riverfront properties were now filled with closed factories and that devaluated the property.
Just being on a river or at a river junction isn’t particularly significant as a geographic determinant. The towns that thrived were entrepôts, places where goods were transferred from one mode to another: rail to barge, or wagon to barge. Since the goods are being moved around in those locations anyway, they were good places to set up factories that would add value, that would turn raw materials into finished goods.
That’s the main reason Cairo didn’t become a big city: once the railroad bridge was built, neither trains nor boats had any reason to stop there.
The only problem I see in them is the issue of flooding.