Keep in mind for all the talk about the horrors of throwing plastic overboard
Its he rare cruiser who spends more than 10% of their time on crossings, so it's just not a major consideration (most spend far less). Most time is spent in harbors and marinas
where access to shore side garbage containers is handy. In remote
areas, burning it on a beach can be an option.
That's before you even touch the perception of having an incinerator onboard (yeah, mostly perception but from a marketing
perspective hard to get over)