Is it really? Single-use plastic from western countries is mostly not the plastic found in oceans. So while they were busy implementing these measures, they do not even scratch the surface of the issue. Do the proponents of these ideas care about the environment at all?
Single use plastic is an eyesore. It's garbage that doesn't stay where it's supposed to.
I agree that supporting developing countries develop better waste management practices would be money well spent, like efforts to support their health systems. Poverty, weak governance and lack of prioritization, in that order, are probably the main impediments.
Projects focusing on the developing or third world will likely be regarded as colonialism, lecturing from a position of power etc, and perception has become more important than correctness or efficiency.
Do you really believe western nations don't use their power to compel poorer countries to act in a given way?
I believe it would be more economically expensive to help another nation recycle than to pass a law domestically and ban/fine for certain disposable goods, but as far as work-effort expended, I think you'd get more bang for your buck to work with those that produce the most plastic. Of course, international processes are always harder than domestic ones, and this isn't an exclusive-or style problem.
On the national politics level it's only almost that bad: we (the US) have very little way to influence what China does with their trash. It might take Trumpish levels of confrontationalism from a Democrat administration to have any impact at all. Sad that candidates aren't taking on this reality... it's much easier to sell a rosy narrative to voters that we can fix everything by making sacrifices at home ala the Green New Deal or somethimg similar.