Bootcamp - No ISO Option
I followed this tutor here and got success: https://www.youtube.com/watch?v=hE8If6gabUI.

The "Create a Windows 7 install disk" option is hidden because your system's capabilities are limited. For instance, older Macs can not boot from external USB disks, therefore creating an installer onto a USB disk would make no sense.

Still, if you want to create an installer on an external disk regardless, all you have to do is edit Boot Camp Assistant's "Info.plist" file:


  
  Open Package content of Boot Camp Assistant app, backup Info.plist file somewhere, then open the old one with XCode.
  Edit file:
  
  
  Edit section's title: PreUSBBootSupportedModels to USBSupportedModels (if it's already USBBootSupportedModels -> skip
  this step)
  Add your System's model identifier(Find it by System Information app) into USBSupportedModels section. 
  Add your Boot ROM version (Find by System Information app) to DARequiredROMVersions section
  Save.
  
  Restart BootCamp
  


A comment of @dusanvf:


  If your Bootcamp crashes after this, write this into terminal:

sudo codesign -fs - /Applications/Utilities/Boot\ Camp\ Assistant.app/