Canals have towpaths because for over 150 years boats were towed by horses. Diesel powered canal boats only began to be used about 100 years ago.
Before the canals were built goods had to be moved on roads that were muddy or frozen in winter and rough and rutted in summer, so slow and bumpy travel. One horse could only pull 1 or 2 tons at a time. On the canal one horse can pull a boat loaded with 30 tons of cargo.
Horseboating was very hard work requiring skilled judgement and experience interspersed with long hours of plodding drudgery. When two horse boats met there were complicated rules about who had right of way and mistakes could be dangerous.
Each working canal boat needed a horse or mule to pull it, (or perhaps a pair of donkeys) and a fly boat working non-stop might need two or three in a day. This needed a large number of animals and workmen to keep all this horseflesh shod, fed and healthy.
Every boat horse needed a stall in a stable at each end of every day’s journey, for a hot tired horse cannot be put out in a cold field for the night, so every regular stopping place, whether warehouse, wharf or canalside pub had to be equipped with stabling.