As you can see its a popular place to hang around and gongoozle or eat or drink. In fact definately the most popular canal side spot in the whole of London. Sometimes you can hardly move, it's so busy.
Then you get a fascinating and attractive place like Three Mills on the Lee Navigation in the East End and its always almost deserted. The Lee Valley Park Regional Authority describes it thus:
Three Mills Island is the jewel in the crown, a cluster of listed buildings and green open spaces in a conservation area surrounded by the Bow back rivers. In the middle of the industrial East End, its main historical buildings comprise of a grade I listed House Mill, the largest tidal mill in Britain and the grade II listed Clock Mill and Millers House. It is also home to Three Mills Films Studios so you never know who you may bump into.
There are good free moorings there too. Always lots of room.
People like to go where people like to go I suppose.