Mayans' Obsidian Arrows not on Plumed Archers

[Mr.America]

Can someone tell me why the Mayan's unique technology, Obsidian Arrows does not apply to their unique unit, the plumed archer? It always annoys me whenever I take them for a spin, that I have to tech into both archers if I want to make full use of their full ability.

[Vonklyce]

Mostly for balancing reasons, same goes for Longbowmen not having access to Thumb Ring, Franks not having Bloodlines, Goths not having Plate Mail, Malay not having Champions and Persians not having Arbalesters and Bracer.
These technologies/bonuses combining with their unique units, would make them just too OP.

[TheDiaper]

Balance, period.

[petercordia]

Also, for the sake of variety.
Currently you can choose between 20% discounted archers with Obs Arrows OR plumes. So not all games with Mayans will be the same.
If you're able to tech into both, it probably isn't a very close game.