When the customer asked for them. Even the Remington era specification sheets, reproduced in The Parker Story, show 2 5/8-inch chambers, intended for 2 3/4-inch shells.
Remington era Chamber Specifications.jpg
The surviving Parker Bros. hang tags I've seen are sometimes quite confusing. Here is a tag for a 1925 vintage gun which shows it targeted with 1 1/4-ounce load but says "Use Shells 2 5/8 Long" --
213855 12-gauge, 2 5-8-inch, 1 1-4 ounce, cropped.jpg
However, our North American ammunition companies quit offering loads heavier than 1 1/8-ounce in 2 5/8-inch 12-gauge shells in 1907. From 1907 onwards one had to get 2 3/4-inch or longer 12-gauge shells for the 1 1/4-ounce loads. The progressive burning smokeless powder, high velocity 1 1/4-ounce 12-gauge loads, Western Super-X, Peters High Velocity, Remington Heavy Duck Load which soon morphed into the Nitro Express, came out in 1922, all put up in 2 3/4-inch cases. Knowing the North American nimrods desire to use the heaviest loads he could lay his hands one, these old 12-gauge doubles digested lots of them from their introduction into the 1990s when we started worrying about such things.