A few things to note about this case.
First, this couple has spent far more money fighting this case in court than it owes in taxes. They are suspiciously well funded.
There is roughly $2.6 trillion dollars in untaxed earnings being held overseas in order to avoid taxation.
US businesses pay taxes on income, but foreign investments used to only be taxed when an asset was sold. This is a massive loophole for international businesses that allowed them to stash earnings indefinitely by moving money from one bank account to another, and only repayriating the money when it would minimize tax liability.
Closing this loophole without a one-time levy would have rewarded corporations engaged in tax avoidance with a $2.6 trillion tax cut.
The Moores did not receive any distributions or payments because they did not want to receive any taxable distributions or payments. That's the scam, to make it look, on paper, like they aren't earning anything while their portfolio grows. Meanwhile, they are free to leverage that value in the form of loans.
This is not a fight between the big bad IRS and a mom and pop investor just trying to make ends meet. This is international oligarchs hoarding wealth in tax shelter nations, and if the SCOTUS rules in their favor, it's going to come out of taxpayer pockets.