Why the global variables info is not shown for Arduino Due in IDE?
There is a difference in how the build system calculates the memory size for AVR and SAM. The platform.txt file contains the rule for calculating the size. There is a difference how this is done for SAM (Arduino Due). 

The AVR size rules (https://github.com/arduino/ArduinoCore-avr/blob/master/platform.txt#L79) are: 

## Compute size
recipe.size.pattern="{compiler.path}{compiler.size.cmd}" -A "{build.path}/{build.project_name}.elf"
recipe.size.regex=^(?:\.text|\.data|\.bootloader)\s+([0-9]+).*
recipe.size.regex.data=^(?:\.data|\.bss|\.noinit)\s+([0-9]+).*
recipe.size.regex.eeprom=^(?:\.eeprom)\s+([0-9]+).*


And the rules for SAM (https://github.com/arduino/ArduinoCore-sam/blob/master/platform.txt#L91) are: 

recipe.size.pattern="{compiler.path}{compiler.size.cmd}" -A "{build.path}/{build.project_name}.elf"
recipe.size.regex=\.text\s+([0-9]+).*


They may be updated to give more information about the memory size. A good reference on the subject is http://www.support.code-red-tech.com/CodeRedWiki/FlashRamSize which shows that the output from size command for SAM contains much more information. 

I assume that from the above information you see how this could be updated. 

Cheers!