I think it's a problem stemming from the game's low difficulty and lack of challenge.
I'll use careers as an example. Moving up in careers from level 1 to the top is easier than in other games in the franchise because it only involves skill grinding as opposed to also having to make friends like in previous games. At launch, getting a promotion involved a list of unique challenges for each job level, which was fun and made it more worthwhile to consider playing the game on long lifespan or with aging off to wack away at a career with the same sim or set the lifespan to short for an extra challenge. It was the most interesting implementation of the job promotion system yet, and I personally really enjoyed it. It added depth to the game and kept coming back to the same sim or playing through all of the different careers in a rotation or through a succession of generations from getting repetitive.
After the update that came out before "Get to Work" released, however, the difficulty of both careers and aspirations was severely nerfed to their current state. This was due to complaints from some players that progression was too hard for them when playing on normal and short lifespans. This not only made careers excessively easy to progress through, but also made every single normal career exactly the same since now the only thing that you need to do to progress is hit the required skill levels and go to work regularly, making every level very samey and repetitive. With the challenge gone, careers have become much more shallow than previous games and less interesting and fun to play through.
Basically, it's the super-easy difficulty and the over-emphasis on accessibility in this TS4's gameplay that is a major factor in causing players to get bored and either quit or go save file hopping. Challenge and a sense of discovery help players feel more invested in a game. When a game has neither, it's hard for players to stay invested for long. So, the only thing I can suggest is looking for mods that restore the difficulty of the careers and aspirations or add more challenging gameplay elements and see if that helps.