Understandable thought. In fact, we used to close all wounds on the battlefield during early wars. But eventually it became clear that closing the wound just traps in bacteria. Bacteria are just like us. They like warm wet places. So now standard of care is to leave infected wounds open and they heal from the bottom up. Best thing for a wound is to be draining and not accumulate.

Source: I’m a friendly surgeon

All wounds have bacteria in them, but unless you've got certain comorbidities, your body is really good at using its own mechanisms to handle that, as long as all the waste products (dead white blood cells, dead tissue cells, loose bacterial cells) have someplace to go. When a wound is "open" like this, they get sloughed off the surface and absorbed by the bandages. No big deal (from your body's perspective). But if the wound is closed, all that stuff just collects in it, and you get an abscess which prevents further healing, causes pain and inflammation, and can lead to sepsis if the bacteria gets into adjacent blood vessels. It's like the difference between taking your trash out on a regular basis or keeping all of that trash in your kitchen as it rots.

Bacteria aren’t smart. They don’t think “let’s go over there to eat”. They go from high pressure to low pressure (lots of bacteria to fewer bacteria).

Basically If you leave the wound open the bacteria can’t burrow into healthy tissue. They are met by a host of immune cells and connective tissue that makes the process hard. If you close the wound you trap the bacteria in a warm, wet space with plenty of food. They will multiply and pressure will build up and start separating the tissues and the bacteria will move into that new area. That’s an infection. If they have somewhere else to go that is no longer an infection. Leave the wound open and it will heal towards to skin, then the skin will heal over the healthy tissue and there will be no pocket for bacteria to hide in. This is a VERY simplistic way of describing the process.

You remove the gauze 1-2 times a day and when you pull it out it takes a lot of the gunk out with it which helps to clean the wound

I think from what i remember, stitching it up is a lot like intubating someone. High risk of infection. Also for draining purposes.

We've been so programmed by movies and TV to think that every single wound needs stitching. Often stitching is not the best option because it has a higher chance of infection. Being able to observe an open wound and clean it multiple times a day is healthier. Though it does create more of a scar and a aesthetically people don't love that

Some people require wound vacs to keep the fluids out of the wound so I would guess that can play a huge part in it.