Why is there a phenomenon of the second construction affiliated?

The most direct explanation is that there will be a market only if there is demand.

Who needs a second-level builder? Construction enterprises, of course. You can't take the project without the relevant certificate, and you need a second-class builder.

If you want to have relative qualifications, you will generally need more than three secondary builders. If the unit recruits full-time, it will increase the labor cost of the unit. Then the unit will choose to replace people with certificates, which will breed. The unit has reduced the cost of employment, and the holder has an extra income.

Although there are risks, there will always be a demand market.