Why do many supervision units also recruit first-class builders? What's the use and need?

The supervision unit does not need a first-class builder's certificate, but the supervision work needs construction experience. At present, the main work of supervision is quality control (domestic), and other controls are basically managed by the owner. There is a first-class constructor certificate, which means that you can directly be the person in charge of the supervision project (nominally not the director). It is difficult to be the person in charge without construction experience. The next builder may have the most certificates in the construction industry, and it is easy to recruit people.