It's always capital investment in brand new manufacturing equipment. You're basically saying, "hey, why not build a brand new factory? Why not build a brand new bottling plant? Totally cheaps!" The ROI is never instant and plastics have to compete against everything else the company could invest in such as new IT systems and other things that could be worth more. You're also talking having to build new facilities to produce the plastic itself. And you're talking about a material that can affect the taste of food, lower the quality of the product, and lower the value by hurting the longevity and repairability. Seriously - plastics are often replacing reusable products that are actually cheaper than all the plastic that is needed to replace them. Shopping bags are a perfect example of this. The actual economics of it aren't as compelling as you've been led to believe. And you've also got the fact that plastics are a waste byproduct of oil refining and oil companies have a strong incentive to push plastics dependency as a hedge against energy market fluctuations.

So it's far seedier than you believe. There are tax breaks, lobbying, kickbacks, predatory pricing, and all kinds of other perverse incentives to push adoption over the finish line. And they 100% rely on the recycling scam to avoid regulations that would have them pay the costs of the environmental damage they cause.

So you have the classic plastics argument that plastic bottles are cheaper to transport because of the high price of oil. But that doesn't factor in that glass is much cheaper to reuse and recycle, bottling plants don't have to be massive centralized affairs, electric vehicles have a lower lifetime operating cost, etc. Instead, oil companies want to sell you plastics as a sort of rebate system for the jacked up gas prices they're charging. Win-win for them.