Why does my dog eat everything off the ground?

Work with them to leave things alone. The leave it command. Also, see if they are stressed. It may not look like it but when you look at what a dog is doing. It becomes clear if they are stressed or not. I had a dog reach for everything around us. Also, does your dog have a toy to get a treat out or a puzzle toy. It could be your dog is bored. This leads them to getting stressed and going for whatever they see. They need something to do at home. Maltese need something to sniff out and get. They are really good finders when they are taught. So a tumble toy with treats inside could help. Also a puzzle toy. At home keep small things out of reach too.

1. Because she is hungry
2. Because she's a chewer/eater
3. Because (for me anyway) you live in a city where the parks unfortunately have picnic food left on the ground.

It's not necessarily an issue until they eat something plastic (chicken wrapper) /sharp (chicken bones)/dirty (old chicken) ----BAN KFC!!

But yes you need to watch them and use aversion training when they gravitate towards a target - ALWAYS carry stronger lures - favourite treat or toy. And work on the leave/dead/morto/drop command - easier to do with some dogs.