Usually this is not too big of an issue when transporting cheap bulk goods, but especially food and other perishables (flowers!) are difficult when it comes to transportation over water.
It's quite curious how the Europe is the only place with real inland shipping networks over water, other regions do not even come close in terms of amount of cargo transported, even though the natural resources are often there. The rest of the world pretty much relies on trains and trucks to transport cargo. There is quite some room for disruption here, but it's a hard an capital intensive market to break into.
EDIT: To come back to your point about people, they often value time quite highly. Not very many people take a ship to travel the world anymore, even though there is a lot of the earth reachable by the sea. Natural resources is only one part of the equation, and usually the trade-off is between time and money.
But other than that, ships (with speeds of up to 100 km/h for fast hydrofoils but rarely for the whole trip) are always going to be slower than trains (usually much faster than 100 km/h).
As an example, Vienna-Budapest used to be served by hydrofoil for a 6-hour trip, which takes 2 and a half hours by train. Calais-Dover is also a good example of how train is faster than ship (30 minutes vs 1h30), even in this instance of a very straight route for the ships.
I like taking a boat when I have the option, but it's rarely actually a more practical option than the train. It can be better than a bus though.
Do Calais-Dover ferries sell things on board? I imagine that the ferries in the Baltic Sea have no incentive to cut journey times, because so much of their profits come from getting people to eat, drink, and buy booze on board. Passengers need time to wander through the onboard shops and restaurants.
And soon, possibly the return of duty free.
That sounds cool, but yes, not competitive unless you are looking for the enjoyment of being on a boat.
More practically, Vienna-Bratislava is 59 or 66 minutes by train, 75 minutes by boat. Depending on your exact departure and destination points, that might actually save a few minutes.
So, unless you are looking for a tour of the steel-and-concrete locks of the Danube, the hydrofoil trip may not be for you.
Having done a few Barge Holidays in the UK on a 72 foot narrow boat the slow speed is relaxing, though doing the Tardebigge Flight (30 locks) is hard work.
Also being able to park the barge in front of the RSC and get tickets to see Kenneth Branagh was a highlight of one holiday