'Work and real life are complicated, and there are always time and budget pressures, so people just don't have the time and attention to pick up on all the things that we notice after the fact.'

Local Authorities (such as responsible for the building here) used to employ a 'site agent' to oversee works in order to ensure it was done to proper standard. He/she would have industry experience and considerable authority. Such a person would be unlikely to turn a blind eye to bad practice.

But this was seen as an unnecessary cost and contractors are now allowed to self-certify much of their own work.

Even where it is a legal requirement for some aspects to be signed-off by another party (such as compliance with building regulations) this can also be contracted out to firms who rely upon the goodwill of contractors for continuity of work. This leads to obvious conflicts of interest and perverse incentives to certify work that isn't up to scratch.