This is what the poster up towards the top of the thread was saying, then another person chipped in with that, "What? You just want to put companies out of business?" nonsense, etc.
To answer your question: there are many ways that the profusion of plastic bottles in our oceans is the drink companies' fault. Most are pretty benign, just one aspect of that business. For example: why do we have plastic bottles in the first place? Most countries still use glass bottles for their soda. Reason: Americans treat their sodas as drinks rather than as snacks. If you go someplace and buy a soda and drink it there, on the spot, and return the bottle, then it can be washed and reused. This is cheaper and more environmentally friendly and really better in every respect than plastic. Americans aren't willing to do this though, they want to take the bottles with them and glass would make that more expensive.
Why do Americans want to do this? It has a lot to do with how we look at labor and time, which makes it possible here and not in many other places, but it's also about marketing: encouraging this lead to more sales.
This does not mean that the entirety of the blame rests on the drink companies. Obviously that person should have recycled their plastic bottle, but it would be better for everyone (except drink company shareholders) if that plastic bottle didn't exist in the first place.