What am I still doing wrong? (Serial Restarting in New Saves)

I wouldn't say you are doing anything "wrong"
but I think what often helps me out of this is doing something completely opposite to my usual playstyle

say for example you always create same type of sim?
how about this time you go and just snatch randomized townie off the street
and start playing them instead making no sim whatsoever?

say you are always building samey house?
well what if your sim doesn't get a house this time?
what if all they have is a tent or bush
or they spend their entire time on community lots?

say you are always ending up with small families?
well what if you played single sim instead?
what if they never romanced anyone?

and so forth :)