On free mobile apps with ads, there's always an option to purchase away the ads. I know Sims 4 is free to play now, but I bought it in 2018. I also own all the packs and kits. Giving paying customers a flashing annoying ad in a hundred dollar game they paid for is not the same as an ad in a free mobile game.
In The Sims 3, store items would appear at the top of your build buy menu with gold borders, and totally cluttered up the game and made it annoying.
I can't even make purchases in Sims 3 or 4 without leaving the game. So if I need to leave the game to make a purchase, ads in game make no sense.
