it's a science thing
the one point where the earth rotates around the sun at that exact point to make it the center of the earths hemisphere to make it at GMT 0. and that once it rotates around the sun, you can tell where there is a +1 or a -1 and so forth; therefore, the G stands for Greenwich, the M stands for Mean, and the T stands for Time; essentially, England is the center of everything since Greenwich is in England. GMT is a term originially referring to the mean solar time at the Royal Observatory called Greenwich which is in London; therefore, in England.
