As simvasion writes this is a personal preference and in this case, it is by design. I am not a fan of it. I would love if the game not touched my sims if I not play them, but enough player loves it to see their own sims in their world and make decisions without their input (as form a new friendship, build new skills and more). I finally just live with it and in my mind these sims just possessed if I am not play them. I don’t think they will change it because enough people like it.
They don’t have to change it. They only need to add this as an option in Neighborhood Stories. The same way you can disable the Stories (stopping Unplayed Sims from changing houses, quitting work, getting married, adopting, etc.) you should also be able to tick a box that Disables Unplayed Households from gaining skills/weight/relationships.
For me it is entirely broken when I live in San Myshuno. The NPCs spam the food stalls, the festivals, and the street performer station and they gain weight and skills non-stop.
