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

@NRowe
Like others have suggested, I plsy rotationally. I play a household till I get bored or tired of playing them and move on to another one on the same save.

I don’t know how many packs you have, but I always pick up new packs as they come out which gives me more game play options. If there are new types of lots, I will add some to my save. When I first started I would also add a new household with a new pack. I play with aging normally turned off. If a new career or hobby comes with the pack I would focus a household on some of the new things.

I would make all of my households different. Like I have a household of 4 single sims in one household. A household with a Mom dad, teen and child in another household. One household might start with 4 young adult brothers and sisters, that break off later but still visit each other. Another household has 2 parents with 2 children, and 2 sets of Granparents that break apart into different households at some point.i have a single Adult with a child, or multiple children. I might have one family with a toddler, another family with an infant. One family might be a Grandaughter living with her Grandmother. I might have 2 significant others without a family. And I also have single sims living by themself, of with a friend.

Give your sims different jobs and different hobbies. Don’t forget little things like making penpals and collecting postcards. Don’t forget to use the club system if you have get together. Even kids can have children’s clubs or teens can have teen clubs. You can make a chess club or art club, etc.. Have your rotational family’s make friends with some of the others. Take pictures with friends. If you have Moschino stuff or Get to work, you have a lot of backdrop options. Send you sims on a vacation to have fun. Send a special Sim or Sims to to Silvadorado if you have Jungle adventure. If you have growing together add likes and dislikes to sims. If you have an artist send him or her out to paint pictures to sell them, same thing with a photographer. I have a photographer with a Buisiness that others visit to buy picture for their homes.

There are just so many things you can do to enrich your game. Download new lots, make new lots. Make new sims. Change the clothes your sims have on, change their hairstyles, send them to community lots on dates. Use different lot challenges. There are just lots of different things to do.

I have multiple saves, between my PS4 and PC. PC has the base game, and only the holiday download and Romantic Garden when it was free. My PS4 version almost has all the packs that I wanted on it.
Back to the point is that Sims 4 can be a bit boring at times, and I can burn myself out on it. If you feel like you are burnt out on the Sims, you can do something else. Doing something else for a bit can maybe help with the boredom, and maybe you can go back to your saves with a clearer mind.
However, if you also feel bored with the family, try to switch things up to appeal to you. The difference between my PC version and PS4 mostly is I usually just have one family, but I will eventually follow that one family through generations. For my PS4, I make multiple families, and am a rotational player with them or just click on them randomly. Also, not all my families are the nuclear family with a dad, mom, and kids. Maybe switching up the dynamic a bit may help as well.
Another thing that makes me interested is putting my favorite characters in the game. I have normal saves with Sims I create, some with nothing but characters I like, and some that are a mixture of both. If I get bored with my normal sims, I may switch over to a character to break it up.
Sometimes I don't play the game, and just look at the gallery for some ideas, as well as playing in the CAS, because I am just getting ideas.
Also, I will make Sims based on other games I play, and make a Sims version of them.