The device known as shoyu-tai (or soy-sauce snapper in Japanese) was invented in 1954 by Teruo Watanabe, the founder of Osaka-based company Asahi Sogyo, according to a report from Japan’s Radio Kansai.
It was then common for glass and ceramic containers to be used but the advent of cheap industrial plastics allowed the creation of a small polyethylene container in the shape of a fish, officially named the “Lunch Charm”.
The invention quickly spread around Japan and eventually worldwide, and it is estimated that billions have been produced.
PLA isn’t food safe in 3d printing mostly because of layers on a print trap foreign material / bacteria and water can also seep into microscopic gaps into infill and it becomes a breeding ground. I doubt it would be useful for anything squeezy but it might be useful for single use forks and other utensils. But paper / wood can do those things already so I don’t see PLA being much use. For sachets I expect the answer is paper with some kind of biodegradable lining which gives a product a shelf life of a few years but does degrade in time.
Also, some “biodegradable” products are only compostable in specialist facilities where it can be shredded and broken down with water / heat / pressure. I think PLA is a bit like that. If you print something out of PLA and stick it out in the garden or even toss it into a compost bin it’ll still be there in 10 years although it might be faded, warped & brittle. Maybe it eventually biodegrades but it’s not quick enough.