Ok serious answers.
As I said before the biggest reason is time constraints. Second is that the current trend is load to near max velocity which is often over max pressure. Read posts on the life expectancy of brass. Most people couldn’t shoot a whole match with a single piece of brass and include sighters. The primer pockets would be loose.
If people thought about it, a very high percentage of people on this forum, either load at the bench or at least the range during load development and between relays at matches. Many take a fired case, wipe off the outside, brush out the neck, size load and fire. The only difference is using multiple cases.
You have to look at the format of the old Schuetzen matches to see why it worked. First they were off hand. Second it was probably more a social event than shooting. It’s not that the prize money was bad, because there were plenty of “ professional shooters”, there was food and beer gardens in full operation for both shooters and spectators. As well as fun shoots that were kind of side matches. Many times shooters placed bets among themselves on these matches as well as the main match.
The shooters were given numbers, at big matches you stood in line, presented your number, the guys in the pits were signaled your number, they posted your target, you shot it, they held up a paddle with the scoring ring number and held it over the bulllet hole. You retired to the loading area an prepared for the next shot. Then got back in line. If you couldn’t read wind and adapt to continually changing conditions, you were out of the money.
Loading at the range is still done today. People still make adjustments on the fly. One reason against shooting the same piece of brass all match long is that neck tension and base to ogive will change slightly between shots. It’s more consistent to have 50 pieces that are prepped exactly the same, than piece that has been changed 50 times.
Some techniques have changed, but the theory is the same. 6.5 creedmoor in a falling block( no relation the the real creedmoor cartridges and rifles) . Shooting a load jammed .025” into the lands will not work well. The block slides straight up and will not force the cartridge into the chamber. As I said before, to solve this a cartridge seater was used back in day. A lever that would sit in the mortise of the falling block with a cam that would pivot forward and force the cartridge into the chamber. Now loading a cartridge that jams, the levering force is done by the cam on the end of the bolt twisting into place when you rotate the lever called a bolt handle. Process the same, technique different.
Back to the biggest difference in matches in the last 150 years is adding a clock, to replace the beer garden. I’m not 100% sure Thats an improvement
Best true answer, people could use a single case and load only it in a match if they wanted to. Most that say you can’t are doing it any way with multiple cases. All they have to do is change from processing the fired brass in batches, and do it one at a time.
Merry Christmas hope Santa brings you a smaller group or an extra X