The 730k is already in bank account, you'd only lose the collateral in case of liquidation, but that doesn't matter because your alternative was to sell it altogether.
You can’t use the 730k then but you are now accruing interest on it, so what’s the point in having it?
So I have 730k in bank account, but instead of using it, I borrow 730k and spend that money (how do you even decide "which" money you are spending anyways, it's all money) and pay interest on the loan? Why would I do that?
Not sure I understand what you mean, you only have 1 730k which you've borrowed. Interest rates are a drop in the bucket (~4%) compared to ~25-40% tax rates and that's ignoring asset appreciation (BTC averages ~300% YoY). If you use something like makerdao, you won't even have to pay a single cent of the debt back as long as you borrow conservatively and don't need your collateral back.