Chicanes on the towpath

I don't know how long I have been arguing for chicanes on the towpath that actually slow cyclists down - and in response the Canal and River Trust have been saying they would rather 'educate' cyclists to slow down.

So imagine my surprise, when exploring the Camden side of the tunnel, to find that there already is a chicane that does exactly what I have been saying they should do.  And here it is.  3 prongs, and a tight enough dimension between them that you have to seriously slow down to get through it, but it doesn't stop wheelchairs, or buggies, or tricycles.  You just can't physically pass through it at any speed on a bicycle.

If CaRT can provide this on the Camden side, why can't they do it on the Islington side, where cycling pressure is at its greatest?