Because the system doesn't care about who is replying, only that your comment has a new reply.
It's the same on the forum side with quotes, if you quote yourself you will get a blue icon.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.