i dont know if it was the reason there, but i always use blocking volumes, if iam to lazy to create a complex collision model in my 3d software. Or when i made an mistake on a collision model
and could “lazy” fix it, with a blocking volume.
from perfomance side, idk also. but i think a collision model is better.
There is no definitive answer as to why exactly that example has no collision for any of the meshes that I’m aware of.
It is a choice that you have when you design your levels though. Since most surfaces are flat and it’s not needed for a specific type of gameplay the flow of using blocking volumes worked well for this project.
If you find that creating the collision mesh is too time consuming this gives you a better option. If you only need a collision mesh for a specific model and not for others this at least gives you a more flexible option to manage and get the most out of your time when developing your games.
Simplified collision within the mesh is usually preferred as it reduces the overhead of placing and managing geometry within levels. Technically there is no real difference though, and dependent on how it was built volumes may be slightly cheaper performance wise because there are likely fewer volumes needed than there are simplified collision primitives required to cover a level. Thus volumes sometimes end up being slightly cheaper.