Lasting generations sounds like BS to me given the arguments against fossil fuel plastic production, banning forever plastics from the environment, and sea and environmental pollution caused by items like bricks or bags.
Why should Lego last generations? A PLA type plastic would be non toxic, break down easier and importantly for Lego, also encourage replacement purchases.
Lego that lasts 10-15 years, with a discount replacement programme, to my mind, is better than 100+ year old Lego killing animals that eat it, or taking up space in landfills.
Anecdotally, most kids don't want old Lego, (just look online at the moms selling old unwanted Lego cheap without instructions or boxes) they want the latest sets, so the justification isn't there either.