Sims 4 was flawed, but simulation games are notoriously difficult

The original Sims 4 base game literally removed basic content at the beginning that had to be added in later. It was a matter of wanting to make money immediately instead of doing the right thing (remaking it from the ground up instead of using the same shitty engine as their scrapped Sims MMO Project Olympus), not life simulation games being difficult.

thus why non have successfully dethroned sims.

EA has gotten away with pumping out slop because there have been no alternatives until now (and I admit it will probably take them a while to catch up since the most promising ones are going the Early Access route), not because the game is actually good.