Why are alto flutes in the key of G?

[jorgevieira]

I guess one has to think first in the desired range of notes. This will determine the length of the tube, and therefore the place of the holes in it, and accordingly, the notes which correspond to each hole or hole combination. This does not exclude a finer adjustment of the tube length such that the flute can be tuned to a more convenient key. This is what seems more likely to myself!
Regards
Jorge