Why I can't use 'startx' command to start X Server on RHEL7 with "X window system" package group?

Issue

• Can't start the X server using the startx command, while the basic xinit command works.

• The server is running RHEL7, installed as a minimal server, only the core and "X window system" package group plus xterm are installed. But when try to run startx command, it fails with following error:

  xinit: connection to X server lost
  
  waiting for X server to shut down (EE) Server terminated successfully (0). 
  Closing log file.
  

• xinit command without any options starts fine, but startx with the default RHEL7 system xinitrc script fails. What is causing this problem?