I think it's a case of paying for someone else's sins. Why should you have to build a case.... It's simple because you want a successful outcome. I'm not saying it's satisfactory but it's just the way it is. I can sense your frustration and its warranted. I wish you well.
It's no racism, and its not just Australia. Unfortunately Thai people have in the past displayed deceptive behaviours. If you can build a case you will be more than likely to be issued a Visa. Healthy, bank account, proof of relationship, successful business, etc. All factors that will influence their decision.
I live up north when I am in town. I can't walk and exercise without the old ladies in the village wanting to drag me in for moonshine. So I exercise in the next village. Every night of the week they want to party. Not my idea of a peaceful retirement.
The secret to a Long and happy life is. Move as far away from the parents as you can. Building on ancestral land...... Really! π² There is a rule, the more bedrooms your house has, the more freeloaders that can move in. If you are a typical westerner it might test your patience.