Not OP but San Diego has this issue. Especially in summer with tourists. My local beach gets disgusting around the fire pits / area closest to the parking lot. I was blown away by the trash yesterday morning when I walked through the main area to surf. People suck sometimes.

I think a lot of the time this is just because there aren't enough bins provided or they don't empty them frequently enough.

Unfortunately not true. They empty the bins daily and people litter literally 2 feet away from them. Unfortunately I think some people just feel entitled to make others pickup after them.

No, its because people are slobs. I see it all the time, people tossing shit into the streets in view of a garbage can.

I can't agree with this. If you can't find a receptacle for your trash take it home and dispose of it there. Being responsible for your own trash seems to me like one of the most basic social obligations for adulthood.