Shortened forms of terms

Why is it that some terms are shortened weirdly?

for example why is activation energy $E_a$ instead of $A_e$
(on a maxwell boltzmann graph)
why is it mixed round?

Equilibrium Constant is $K_c$ dunno what happened there lol

How is it weird. E is standard notation for energy, so why would it be easier if this one form of energy suddenly became an A subscript E when everywhere else forms of energy use big E. And K is just a constant, the subscript c stands for concentration

Ah yes with kinetic energy too >.>

i just think it's more logical to use the Letter in the order which the appear in the term so

Kinetic energy
$K_e$
instead of $E_k$

That isn't easier at all. You would have equations with like 7 different abbreviations for energy in, and you would have to remember them all, whereas you can look at any eqaution with energy in and know that it involves energy, and then the subscript tells you what form of energy we are dealing with

so it's a sort of convention thing?