Do you have LotFullOfSims installed to overcome that limit? Probably!
Now there's a better way: remove LotFullOfSims, and install this mod in stead!
It's tiny, it works for ALL games, and it does NOT conflict with ANYTHING!
Why would you want this one, if LotFullOfSims already works well enough? Well, for one thing, Unlimited Sims works with all games, and also with all versions of TwoJeffs' PregForAllGenders. And that's good, if you want to install the P4A - Alien Trigger Override
Any settings you may have in your UserStartup.cheat file to accommodate LotFullOfSims, are still useful for adding families from neighborhood view. So you can leave them where they are.