<p>As I understand it, cover identities were originally constructed for members of Team Machine, most of which are "static". That is, Shaw's "identity" has been set (much like hard-coding) as a department store salesperson (at least by day), Finch's identity is set as a professor, and Reese as a detective. Although Reese has been involved in a number of interesting shooting incidents, he has managed to keep those related enough to his cover to remain believable as a detective, and likewise Finch has continued to function as a professor.
</p><p>However, once Samaritan's human agent established a link between the person who pulled off the Marburg heist (recall that whole affair involved "relevant" numbers) and the somewhat random woman who was supposedly moonlighting as a "wheel-man", she became linked to something at a much higher level than an ordinary ring of bank robbers, and her identity as a salesperson became untenable.
</p><p>Root is different; her identity is fluid, and something the Machine changes every few days or weeks according to her "assignment", for example reporter, nanny, investigator, chef, etc. For her, the cover profile is not hard-coded but dynamic, and in a sense more challenging, as she is continually learning new identities. The Machine has probably assessed the relative capacities of its agents, most of whom could not sustain what is required of Root.
</p>