The Build Mode features in 4 are pretty good if you’re into virtual dollhouse building, and there’s a ton of custom content for it (as long as you’re on PC).
Live Mode is not very good, but it’s functional enough to play dolls in the houses you built if you’re willing to do all the story writing to make up for sims not having very interesting personalities/desires/autonomy.
It is part of the main gameplay loop. In order to keep your car in a state where it protects you and is reasonably driveable, you must gather materials to craft repair items and replacement parts, in order to maintain the car’s panels, doors, and bumpers (which together function as armor), its wheels (which are necessary to get anywhere), and the various add-on systems you can craft for it. Tools gradually break with use, so you’ll also craft replacement tools, which are mostly for scavenging materials or interacting with stuff in the Zone.
By collecting a certain resource you gradually unlock upgraded parts and tools for crafting, which is the main way player power progresses during the game.
Even if you buy a DVD, the only thing you are “buying” is the physical media and a license to operate the softwate. You don’t own the software stored on the media, you must use it in accordance with the license agreement or potentially face legal action. The main thing about digital storefronts is that it’s easier to revoke the license.