Makes sense. They have metaphorically hundreds of DLCs each priced like a full game. There is no complete edition and they almost never put anything on sale.
If you want a complete copy of Sims 4, a game that was released one decade ago, it will run you just under $1,000 USD
This is why I'm over the god damn moon that there is finally some competition coming along, so I have an alternative to this soulless, broken, expensive piece of shit, that isn't just an older entry in the series.
Still I can hear some executive saying there shouldn't be a cap on how much whales can spend in the games. DLCs are limiting revenue. Instead, there should be something you can buy as much as you want without ever being satisfied
The Sims 4 is the only game genre I know of that doesn't have any alternative game. There's especially no open source alternative game. There isn't an ethical indie studio equivalent but also not even a different scummy AAA studio has a simlike game.
Starting some kind of sprite based isometric graphics sim game seems like the kind of thing that would make a fun hobby project but personally, I prefer to spend my time doing hobby operating system development. I won't be the one to make such a game but I'd make mods for it.
Maybe look into the Flare engine. One might be able to use that for the isometric graphics and clothing layers. If that isn't quite versatile enough, there's always Irrlicht or Ogre Engine.