It costs about $5,000 or $6,000 per metre. In other words, it can cost approximately $200,000. People can't afford to do it.
The work has to be done by experts, if you want it to be innovative and sustainable and not disrupt biodiversity. You also have to consider water quality and heating.
You shouldn't just use riprap, since it accomplishes absolutely nothing and is inhospitable for wildlife, plant life and people.