It is free because there is so many expansion- and gaming packs. It's also said that the Sims 5 is coming "soon". There is soooooo many mods. Some of the mods are bug fixes and to upen up more functions you don't have in game play.
But there are also a mod that are about killing your sim in all of the worst way. HAHA. It's so much to chose from. I just read about the WW (Whicked Whims), and I think you should google it instead of me telling you. If you are 18+, Haha! I haven't tried any mods yet, only some bug fixes.