Why is the Taiyuan subway conductor officially compiled, but the security check is not?

Employees hired from external security companies. Official website of Taiyuan Metro shows that security inspectors do not belong to subway employees and do not enjoy any treatment of subway employees. The daily work of these security inspectors is managed by the subway station, but the security inspectors are employees employed by other security companies outside the subway. Taiyuan Metro is an urban rail transit system serving Taiyuan City, Shanxi Province, China and Taiyuan City. Its first subway line was officially put into operation on February 26, 2020, and Taiyuan became the first city in Shanxi Province to open rail transit.