Bart,I'm sure you have the answers and I will be some percentage wrong.
Why do the manufacturers do things the way they do? My guess is,There is more than one way to skin a cat.
There might be different priorities or upstream factors.
Sierra has had the priorities of sleek form and top accuracy. I do not pretend to have the bullet making knowledge of Sierra. A disruption of the smooth jacket surface may cause some turbulence.
Lead is "deader" than the copper jacket. Forming the groove may actually create clearance between the lead core and the jacket.
With match components, Sierra would control the quality of the jacket and core so a canelure might be a solution to a problem that does not exist.
Making military ball ammo will probaby have more variation so a canelure might crimp the bullet to the core.
The practice of crimping the case neck to the bullet can cost accuracy.Its not a universal practice for match ammo.
Trying to crimp a non-canelure bullet at the case neck leaves no place for the crimp to go. The seater die will produe poorly controlled distortion of the jacket and core.
Speer and perhaps others solders the core in with " hot cor" I think there are some jackets electro-plated.
In some cases,the canelure may be about terminal ballistic performance. How the bullet expands or holds together on game.
I don't know that there are simple,one answer fits all as to "Why" there are canelures.
In some cases,I'll speculate a canelure may be for no other reason than to meet a Gov't spec. In some cases,having or not having a canelure might be about marketing. What s the story behind Remington Cor-Lokt ? Its a popular bullet with loyal following.
IIRC,Speer makes a 30 cal bullet specifically for the 300 Savage,with a cannelure placed for a crimp at the right location for 300 Savage.
Given the short neck and the Rem Model 8/81 semi-autos,might be a good idea.
I would guess the elimination of the canelure on military match ammo might be related to asphaltum.
Some believe (and it may be true) that a light crimp with a collet crimp die utilized with a canelured Match King might improve uniformity of ignition.
I don't know. I'm not of the "crimp school".but it takes testing to prove.
Match bullet jackets are typically thinner. Handle with care.
I'm always grateful when you teach me something new.