Kits have probably worked better for them during the pandemic and with their current staff of people. They can make them in a shorter time and with gameplay kits now gone (they removed the category from the main menu) they don't have to focus on gameplay with them either.
We might see stuff packs again someday but I think it will be difficult with their current release schedule which seems to consist of 4 seasons in a year with base game updates, SDX, 1 pack and 1-2 kits. The only way they would be able to do that would probably be 1 stuff pack with several kits during a season and that might not be a popular decision.
My guess is that they have Lost Astral in full production, and other games like The Sims 5 in pre-production. The Sims 4 will be around for several more years and will finance their investments into their new studios.
I'm hoping that we will hear or see something in 2023.