Because I take Jubes' word for it. He is not a liar. In fact, quite the opposite. He tells the truth, sometimes to his own detriment. imo
You will notice 'the last known person to see William alive' is not mentioned anywhere - but now Jubes has mentioned it because he is sick and tired of their investigation being criticised and his SFR being attacked.
Lindsay has always been protected. imo (As she should be.)
She is mentioned as little as possible, we have only heard little snippets of her statements. I think mostly to say that Lindsay doesn't know what happened, that she didn't know any hidey place William might be, and that she saw a car that looked like daddy's car. Because everyone was wondering what Lindsay saw.