New builds will already come with a guarantee. In the short term the developer will send someone to fix issues and may well still have people working on site. In the long term there will be insurance policy. But it just happens that there is sometimes an economic incentive to accept lower quality in order to meet some other objective. Maybe the electrical contractor put in a low bid and wants to finish the job. Or maybe the developer is running low on cash within the project budget. Or perhaps the project manager is under pressure to hit a target.

Developers are just like any other complex corporation. Quality is just one thing that has to be balanced. And it is a market with massive pent up demand and buyers everywhere. And customers who have very little choice after they have signed on the dotted line.