It is ridiculous that co habiting couples are still discriminated against in this day and age.
Hardly. Discrimination would indeed be an appropriate word if cohabitating couples were denied the opportunity to get married. This existed for same-sex couples prior to the marriage reform referendum and the introduction of civil partnership.
It existed in spades for separated people prior to the divorce referendum. But now? Seriously? There is no bar to anybody choosing to get married (apart from finding a willing partner!) and availing of the advantages of marriage. Of course it also comes with certain responsibilities which some might see as disadvantages. The responsibility to maintain the other spouse, restrictions on alienating the family home, implications on divorce, etc etc.
Point is (civil) marriage comes as a package; everyone can opt to buy into the package or not - it's a free choice. I don't see any discrimination here. The absence of a right to design your own version of marriage and the package of legal rights and responsibilities that go with it is hardly discrimination. If it is, I'd like the right to design my own package of rights and responsibilities as a taxpayer, please!
I was in Australia in 2021/22 and they had "de facto" status for co habiting couples. Why haven't we introduced something similar?
Because people should have a choice. "De-facto" status, or even better de-jure status, is available simply by signing up. Fast, cheap and accessible, if that's what you want! If you don't want that, it's hardly the business of the State to impose it.
Through my work, I have been able to point out the dire tax consequences to couples if one of them dies and they are not married. These tend to be couples that have kids together. Yet, they are treated as strangers in the eyes of the law?!!
Again, it's a choice thing. Are any of these couples not allowed to get married? I think not. The State has done its duty by allowing them to marry. We don't need nanny-stateism to second guess their free choice. Especially if they make that free choice after excellent advice from your good self!