Primarily, it's been the lack of a decent base game.
I have restarted my game, or put them on hold waiting for base game content and for certain expansion packs.
I've restarted three times.
1st time:
I tried playing a family when we first got The Sims 4.
I really disliked how babies skipped the toddler stage and went on to be children. And I disliked how old the teens looked. It looked like they skipped the teen stage and went straight to being young adults. So I took my sim from CAS and only played young adults and skipped raising families altogether.
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/Game%20Play/05%20Twins/09-19-14_10-00nbspAM.png
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/Game%20Play/05%20Twins/09-19-14_1-22nbspPM.png
2nd Time:
The second time I had continued playing my young adult sim and she had amassed quite a few CAS created friends and I enjoyed playing them. But we had Get to Work and Get Together now and my play up to that point had been pretty random as I added more sims to the rotation. I decided to start them all over again.
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/Game%20Play/34%20Happy%20thread/12-12-15_7-12-17nbspPM.png
3rd time:
We finally got toddlers and we also got Parenthood. I finally felt I could start playing families now.
But instead of hooking up my young adults with each other, I aged them all down to toddlers in CAS and gave them parents. Now they will get to grow up together and go to University together (When University finally came along.)
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/A%20Mega%20Reboot/17%20Story%20Progression/Melonie%20Bloom/12-09-17_9-54-38nbspAM.png
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/A%20Mega%20Reboot/30%20Everybody%20is%20Onboard/07-03-18_10-11-49nbspPM.png
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/A%20Mega%20Reboot/31%20Banks%20pt2/07-08-18_4-43-17nbspAM.png
http://i46.photobucket.com/albums/f116/cireking213/The%20Sims%204/A%20Mega%20Reboot/30%20Everybody%20is%20Onboard/07-03-18_8-03-53nbspPM.png
The fourth time:
Has not happened yet but it is coming.
When all these sims have graduated Uni and are in their starter homes and apartments, I will set this save as a master save.
And I will use it when I want to start a new game. I will probably use the master save to start new saves so I can focus on a few household at a time, because I have probably over two dozen sims that I really like in the world. All in all, my CAS sims, plus the dormies they met at Uni, plus TS4 townies.
However, the 4th restart is a ways off.
Only a few sims have graduated Uni and the next half-dozen are teens in prep-school and the rest are still children.
https://hosting.photobucket.com/images/f116/cireking213/01-03-21_12-34-25_AM(1).png?width=1920&height=1080&fit=bounds
https://hosting.photobucket.com/images/f116/cireking213/11-07-21_5-31-25_PM.png?width=1920&height=1080&fit=bounds