I'll be honest and say I stopped picking up other peoples' trash for the most part. I used to carry an extra bag for it. There's just too much. I gave up with it here in the Bay Area. In fact I rarely fish here at all now anyways.
Diapers, beer bottles, corn cans, bass bait packaging too. Diapers are a biohazard, not touching that.
However, if I'm hiking/backpacking somewhere and I see something I grab it. Why? Because I rarely see any even on popular day-hike trails. Two pieces of "trash" in 6 months, one a trail map, the other was a tiny piece of blue tape from nearby trail maintenance. It doesn't feel like a lost cause.
I think the environment and nature is more central to the hiking community (tree huggers oh no!) because I rarely see trash on trails, even ones that are right next to lakes I fish (Calero Res for example). Shore is littered, trails 100 yards away are pristine.
Why? I think more dirtbags fish than hike, short answer.
I think people here on the forum, since we are into fishing enough to actually BE on a forum, perhaps we are less prone to littering and more prone to following the laws and giving a dang? We discuss this stuff here at least. A litterer may join the forum, read all the complaints about it and quietly stop doing it. Maybe, I dunno Not many dirtbags here.
California is filthy anyways so it ain't fishing that's the problem (not even close don't get me wrong). Just saying I don't see it on the trails even miles out.