(a) The massive plastic producers are multinational oil companies, and they see it as a growing industry to capitalize on, so they are extremely influential lobbyists for maintaining plastic production.
(b) Anything that makes shipping lighter, cheaper, and generally more viable will result in much more shipping and thus much greater emissions, not less. This is always the problem with efficiency-driven arguments. (But it takes understanding the complexity of systems to understand this.)
(c) Of course the ecosystemic outcomes are devastating, and we still barely have the knowledge to understand the full impact.
Here’s a quick article if you want to educate yourself a bit more, I’m not going to keep replying: https://www.theguardian.com/environment/2021/may/18/twenty-f...