This clear plastic capsule is called a preform. Plastic bottles of all shapes and sizes start out as preforms like this, which allows them to be shipped to the bottling plant much more efficiently.
Bottling plants then use a vacuum mold to heat the preform until it is soft and pliable, and hot air is forced into it, causing it to expand into the shape of the mold. After it cools, the resulting bottle is recognizable as drink bottle, such as a 2-liter, with up to 40x the volume of the original preform. It is then filled with a liquid and stocked on store shelves by the thousands.
Single-use plastic bottles are notoriously bad for our environment since they are one of the most littered items in the world and only about 9% are recycled. This bottle preform was taken from a production line of Coca-Cola, the biggest plastic polluter in the world.
We like using preforms because they are nearly indestructible, so they don’t need to be single-use. You can use them as test tubes, to safely transport liquid samples, to propagate seeds, etc. And you can just pop it in the dishwasher between uses.