The plastic bottles used for soft drinks do not provide the same level of protection from oxidation as glass or aluminum containers, which can significantly impact the shelf-life of alcoholic beverages.
Plastic containers designed specifically for beer are generally more expensive than glass and thus rarely seen in the United States.
In general, beer is not sold in plastic bottles simply because the bottles themselves are more expensive to produce and are often less effective at keeping the beer fresh with a long shelf life.
Plastic bottles can save on shipping costs, and the difference in price between glass and plastic decreases as the size of the bottle grows.
The main worry with plastic bottles is increased oxidation. Still, larger producers move quickly enough and with enough safe handling practices that this isn’t an issue until after it reaches the consumer.
Stable PET plastics are a must since reusing LDPE or HDPE bottles will severely impact the flavor of your beer through plastic leaching and oxidation.
With proper storage and handling, plastic beer bottles can have the same shelf-life as glass bottles: 6 months to 2 years.