It's because the brute is so good at pretending and doing things in secrecy that the actions for which he deserves ten strikes of lightning go unnoticed by anyone.
When the investigators go to investigate, the neighbors all say he treats the child well, never hits him, often takes him out to buy treats and such.
The brute then explodes with his acting skills again, pretending it was just an accidental, one-time act. With only Qian and others witnessing it once, along with Weiwei's unilateral accusation, the evidence is insufficient.
The situation is already making Liumei and Qiuqiu anxious and angry, yet Qian seems unfazed and keeps her composure, attending treatments and classes regularly. Oh, yes, lately she's been locking herself in her room, tinkering with bottles and jars. Liumei asked her once what she was doing, Qian smiled and told her she was studying the effects of plant essential oils on animal olfactory senses.
