I suspect that some of the regulatory environment here is the shape it is for historical reasons -- canals were originally commercial waterways with heavy traffic, not a more lightly-used pleasure/leisure environment.
The comments responding to you don't make any sense either. Needing some sort of permit to permanently moor a houseboat is totally different from having to pay to use a canoe or inflatable in the water.
In case there anyone wants to defend the UK's absolutely idiotic licenses, here's a concrete example from your neighbors about 100 miles east.
Here in the Netherlands we have a ridiculous amount of public water - canals, rivers, lakes, etc - and it's all entirely free to use. It's even free to moor your boat temporarily (up to 3 days) at thousands of spots around the country. Our population density is double, we have more people with boats, and we have a massive amount of commercial shipping traffic everywhere. We've got several of the busiest ports in Europe. One of them is as big as ten of the port of London! And somehow it works out splendidly.
This only covers privately owned “boats” if you rent a kayak or a canoe or a boat the operator must have a business waterways license which will enable you to use the waterways for the duration of your rental.
Paying 48 pounds (63 USD) per year for the ability to use my cheap inflatable on the inland waterways is preposterous. That's more than four thousand US dollars added up over a lifetime.
The cheapest/shortest license I could find was a princely £9.10. Fairly frequently I've gone out for a brief little trip - an hour or so with the boat, drift down a canal, get some lunch - with my girlfriend. Now in order to do that I need to fill out a multi-page form and pay someone £9.10? Ridiculous.
Why can't it work the way it works here? We have more waterways, more people on the water, more commercial shipping, and a substantially more involved system of canals, lakes and rivers, and it's totally free to plop your little inflatable wherever you please (excluding a very small number of areas only available to commercial traffic, far from where anyone would want to be in an inflatable.)
By the way, I've been to the UK, and your waterways are disgusting - certainly worse maintained than here in the Netherlands. I've seen heroin needles, human feces, and piles of trash. Meanwhile over here we keep our waterways clean without making people pay four thousand bucks over their lifetime for something as simple as an inflatable boat. This is despite the planeloads of British tourists coming to the Netherlands to throw trash in our waterways.
Can't speak to the UK but in the USA, maybe. In my state, if it's a "managed" lake or reservoir, or in a state park or forest, there is a watercraft license requirement. Natural lakes, streams and rivers are exempt.
It's a leftover sentiment from the days when taking anything of any usefulness or value from the land without permission was considered stealing from whatever lord or nobleman owned that land. Licensing for everything and everything is not considered abnormal when it's the status quo going back a thousand years. Society takes a long time to change things that are deeply ingrained like that.
edit: If there's an alternate explanation I'm all ears...
The main beneficiaries of the license fees in England and Wales are the British Canal Trust and the Environmental Agency both of which use the money to maintain the waterways and the environment around them.
The fees are next to nothing for smaller vessels, for unpowered boats the fee is incorporated into the membership fees for the clubs.
Rentals are exempt as they fall under the business fee of the rental provider and visitor licenses are available for short term that cost next to nothing.
These waterways are accessible upon payment of a licence fee, ranging from a few pounds to over £1200, for use by boats, canoeists, paddleboarders and other craft. Walkers and cyclists can use the extensive network of 'Public Rights of Way' that run alongside the canals and rivers without payment of a fee, which were previously permissive towpaths.
Do you need a license to just float down the river on an inflatable? Also, if I drop something into the water, is it now property of the trust? What a ridiculous governing body. The UK really loves licensing the shit out of everything.
"Oi, you got a license for that license, mate?"