Why ksh get error of "limit exceeded"?

Issue

• The user add some ulimit into /etc/profile:

     ulimit -u 278528
     ulimit -n 65536
  

• But got error after switch to the user by su command.

  # su - testuser
  /etc/profile[86]: ulimit: 278528: limit exceeded [Operation not permitted]
  /etc/profile[87]: ulimit: 65536: limit exceeded [Operation not permitted]