This is interesting. It was not always like so. Order of availability by plastic type, roughly:
P1 D, Rpro and C. S?
P2 D, S, P, G, C & glow. X. This guy has it all.
MD1 SG, D?
MD2 Rpro, P, S and C?
PD first S? Then P and later C? Glow. G.
CD first D, then P and S about same time? Now there are a few C-CDs too but not regular.
TD first D, then S, then C?
PD2 went C, P and S, in that order, right? Glow too.
DD2 was in Echostar first, P C and S in some order. Now G.
FD S, D and C. G.
TD2 went S, C. Kind of a sidenote mold.
MD3 C, glow and much later now P
P3, D then C. Glow.
FD2 only C. Glow.
CD2 C, then G
P1X D and X almost simultaneously.
I am just typing this off the top of my head. Pls fix if you know how. Def seems like a historical pattern now where C-line is the norm. P-line has now only resurfaced in MD3. Before that the latest were P2 PD2 and DD2 so it has been a while. I think a lot of people would appreciate the missing links in P-line or barring that, S.