There are a lot of things to enjoy about the hobby. I grew up with the railroads so I got hooked at an early age.
I have been puttering around with my layout for nearly 30 years. There were long periods when I went for a period of a few years and didn't even go into the train room because where I live we don't have any hobby shops making it extremely hard to get anything done. When internet retailers became more numerous I was able to move forward.
Now I have finally been able to get all of the track down, probably over 90% of the scenery done and have probably more than enough locomotives and rolling stock, I am finally able to operate the way it was designs for, mainly switching. I did enjoy many phases of construction. Scenery. Learned a lot as I hardly had a clue when I started it. Scratch building. Never did that before either. After a few structures, it almost became second nature and it was a lot of fun to build structures to fit into particular spaces.
Custom Painting. Never held an air brush before in my like until I decided that I would freelance and wanted to custom paint my locomotives and freight cars.
Weathering. Never did that before either. Why would anyone want to screw up a perfectly good looking freight car? I don't go into heavy weathering, but do like having equipment look like it has been around for a while. I got to the point where I wouldn't put anything on the layout until it was weathered to some degree. Years ago I used to go up to Great Falls, MT during state fair and help the model railroad club up there for their open house during fair hours. Brought my weathered equipment down there and the club members heard numerous comments on how the cars looks so real. All of the club members cars were not weathered. The next year, almost everyone had weathered cars and locomotives.
I can now enjoy operating the the layout the way it was designed, I'll go down to the train room to do some minor work on the layout and in a lot of cases nothing gets done because I am running trains and enjoying every moment of it.
There are just so many things about the hobby that I enjoy.