Reducing liquid weight in trash

In the old roll of film I recently developed, I found this seemingly mundane photo I shot in Tokyo.

I was having coffee with my sister at a Starbucks that day. As we were about to leave and throw my ice coffee cup away, she pointed out that I should pour the remaining liquid into the a separate trash can first (shown above). It made immediate sense to me. By taking the liquid out, the trash weighs less, it's easier to take out, it emits less carbon to haul the trash to the landfills. I already pour liquid out from containers before throwing out bottles at home as many of you might as well. So why isn't it more common in commercial environments? All the sodas swishing around in tightly sealed garbage bags probably gets broken by the time it gets compacted on the back of garbage trucks but that water weight gets carried to the dump, wasting fuel. It seems like a good idea that we can quickly implement in this country as well.