Venetian potential of the New River

Does anyone know why...

When they built the bridges over the New River (the section that passes through the ladder), they made a lot of the walls (e.g. on pemberton) just high enough to stop people looking down it? Seems a bit mean. Is there a historical reason?

If a few rows of bricks were knocked off the top of every bridge, it would open up long views down the middle of the ladder and add a hint of Venetian glamour to Harringay!