It's not because it is a new game, but because of the impact it would have depending on the xml. A single tuning that turns off autonomous playing in the sprinkler is not very likely to conflict with something else. Sims 4 also has some tunings that are extremely specific, where I wouldn't be concerned with potential conflicts.
But something as central as e.g. the list of interactions for a sim is not something I'd feel comfortable changing for a random little mod. For me this is a big deal. It would have been quite an annoyance in Sims 3 if I would have had to choose between DebugEnabler and MasterController and Woohooer. It's not just a matter of forcing users to choose, but it could also have the effect that as soon as there is a widely used "must-have" mod out there that changes the sim interaction list and/or the general object list, modders will be discouraged from publishing/creating smaller interaction mods, because they know it's unlikely that someone will give up a "must-have" mod for a nice-to-have one.
An alternative to the scripting approach could be a mod-merger that collects the new interactions from various mods and merges them into a single instance of the sim_object resource or the objects.base_interactions resource with the global_affordances list.
