It's for the best that we make sure to follow these rules as best as we can. If Maxis has to enforce it, then we risk them having to ban all mods in the sims4 because when we make mods, we are modifying and selling something that is not our own. When you buy a game you buy the right to use it, not modify it and resell it.
Some mods work completely outside of the sims4, but even then, the modder would probably have to ask EA specifically if their mods can be used in order to not break the Terms of Service Agreement.
Modding has always been a gray area of what is allowed and not allowed, and while I am pretty sure that Maxis likes mods, I'm not so sure EA would like it if there would be actual costs involved, like having a team that enforces these rules.