For me, there are three main reasons to build modules instead a home layout: Space, flexibility and they are achievable.
Modules take up less space
Modules are flexible
There are two aspects to this: The layout itself and the focus of your modelling interest.
If you like this flexibility, building modules and joining a club might be a thing for you.
A Module can be finished
There is even more
I consider these factors as significant, but there is more. Attending a modular meeting is a lot of work and it even is exhausting. At least for me, making friends and having fun with them is even more important than working on the modules itself.