There are limits to how many trees, how big they can be and how close to the house you can have them. There is also a ton of car infrastructure that needs to be spread out across all the houses that takes up a good percent of the land no matter how you slice it
The most important difference though is that each person only has access to their stamp of nature that is 1% of the island. With the apartment all 100 people living there have access to 96% of the nature on the island.
It doesn't have to be just nature either. You can use it to build playgrounds, outdoor gyms, running tracks, community centers and tons of other public use things.
What part of this makes it look like a trailer? Is it the brick wall or the railing that is there to stop you falling down to the second floor.
I think 2 story brick trailers are just called houses.