It is so terrible that builders are so poorly protected ... unfortunately, nothing has changed about this for decades ... main contractor bankrupt, new company: it goes on
A completion bond protects against the insolvency of the construction company. Ultimately, it is an insurance, like builder's liability or construction all-risk insurance, which can also be useful for construction projects. By the way, it is standard practice with large, well-known general contractors, e.g., with the low-cost provider TuC.
As a taxpayer, I am very glad not to have to finance security systems for private builders. Private enjoyment may gladly remain a private risk.