It's literally convenience trumping everything. For example, for gatherings (back when we were able to have those), you could either bring a big jug of water a

It's literally convenience trumping everything. For example, for gatherings (back when we were able to have those), you could either bring a big jug of water and a bunch of solo cups, a case of bottled water, or, the eco-friendly option, a jug of water and just assume everyone else will have a reusable water bottle (e.g. Nalgene). The easiest option there is the bottled water option. This can only be solved by shifting from the "wish upon a star that all consumers will somehow solve the problem themselves" strategy to putting the responsibility squarely on the shoulders of the people profiting from putting municipal water in single-use plastic bottles.