Why are capital appreciation bonds (CABs) a controversial way for local governments to finance projects?

See explanation section

Explanation:

Municipal security from which an investor will receive a return on investment from an initial principal is called a capital appreciation bond. However, in this security, the return on investment will be reinvested further until the security matures at a specific rate. The primary purpose of the CABs is to permit the local authority to generate revenue. Due to the financing in the innovative project without increasing the tax is one of the controversial ways for local governments to finance projects. Another controversial way is to owe investors more than what they acquired.