It really has nothing to do with money since it is a communist country. The government could decide to allocate resources (ie: people) towards dealing with the mess. That's effectively what they do in the cities.
In Saigon, I lived on Truong Sa in a 5th floor apartment. This street is along a river running through the middle of the city. Every day, there was several boats that would go up and down collecting the trash that people would dump into the river. All day long, I could watch people just stop their bike, get off, walk over to the river and dump their trash into it. The lazy ones would just dump their trash on the street or in the gutters, which tend to back up during rains and cause more flooding.
oh dear, thats so gross
Picture of some random beach somewhere... whole entire coastline is trash and Vietnam is shaped like and the size of California... https://imgur.com/fp6D7Ca
When I went to the world heritage site, Ha Long Bay, I went out in a kayak and picked up a whole bag of trash. I didn't even need to take a bag with me because I just found plenty floating around to use.
This is also a country that still eats dogs (and cats) and really anything that moves. You won't ever get them to stop making waste. https://imgur.com/ItvSF6T
Are you maybe saying it a cultural thing? As in, it would be too difficult to convince people to pay somewhat higher taxes and then adhere to littering/dumping/burning laws?