In other words, why Arduino IDE does not have an interface similar to avrdude GUI? Considering that one of the goals is to support other AVRs as well, I think is time to have the required tool to upload the .hex files.
Why we need it... Imagine that maybe I'm making boards for others, boards which use different ATmegas and I need to upload hex files to test the board functionality, frequently switching from one ATmega to another (and obviously, from a hex file to another). For those hex files, I need to compile only once. But there can be various scenarios...
For the start, it will be good to have a GUI interface to Optiboot bootloader.
BTW, Optiboot bootloader support ATmega168P
which is not yet supported by Arduino IDE and such interface will help if you decided to go beyond Arduino language.
A funny thing: the users of MPIDE wants the same thing