My guess is that the family very much isolated themselves once Lacey got to a certain point in her deterioration.
I appreciate your analysis of what could have caused this level of neglect, so tomatoes thrown from me, but the more we learn, the worse it gets.

From the link…
Neglected woman who died on parents' sofa starved to death, had not seen doctor in 20 years
Fletcher's parents, Sheila and Clay Fletcher were described as the church-going type and were always out and about. Lacey died Monday Jan. 3, 2022. The weekend before, the parents were out of town the WBRZ Investigative Unit learned.
"They go to church every weekend and do anything for anybody," Neighbor Robert Blades said.