About fairy pieces

So,archbishop,general or dragon bishops are a combination of two or more pieces.But why do they need their own letters?We can name archbishop to BN,or dragon bishop BU.

Using two letters can actually free these letters:A(NQ)E(NR)H(NB)J(II)L(CC)M(NK)O(NN)T(SS)V(NC)Y(SI)Z(SSII,also TJ)Δ(BU).

or if let rook as a wazir-rider,we can free them too:B(FF)K(FW)R(WW)Q(FFWW,also KK,also BR).

to name a teamed pieces,name it simply like rNC(rV,red's wildebeest)

use a comma or a space to separate them when typing a promotion,like NQ,NN,G,B,NU(pawns promote to an amazon,knight-rider,grasshopper,bishop or dragon bishop.)