This is how I see it too. One of the functions of money comes as a store of value, and this is also tied into a Marxist view of value as being a real social relation at play. Beyond money simply having use because its used in taxes, money is an instrument for expressing and mediating value; and value also allows for the reallocation of labor in society - the source of value itself - through the law of value.
People want something that can hold on to its value across both time and space. Sometimes this store of value isn't money (think houses or famous paintings), but a form of money that acts as a reserve of value is always in need. And money which can serve as an expression of value thanks to the strength of the government (or an enforced tax) may not be seen as a safe storage when trust is shaky. Anwar Shaikh (though be mindful that he is rather anti-MMT) describes this as a flight from more virtual forms of money to forms closer to actual value in moments of crisis, where gold tends to be the (extreme) end-point of that flight.
There is historical trust that at least gold will be seen as something valuable in an unknowable future with unknowable governments and monetary systems. Some may go with beans though. But gold, or some other commodity with a level of acceptance, has value as it's a product of human labor. So when looking for a store of value some people go with it due to historical legacy and the real value embodied within it. There's a reason that even national banks are buying gold (amongst other commodities and baskets of currencies) as they dedollarize.
This isnt meant to be a goldbug argument for going back to the gold standard. It is instead a reminder of the existence of value and one of money's function of a store of value. I'm not (completely) against MMT and think there is a lot to it to learn and that is true and descriptive. But it can't mask nor cover up value as a real social relation. And most MMT'ers I've talked to seem to ignore value. I suspect it is a reflection of the academic training of economists, even MMT academics, to do away with value as a useful or necessary concept, but I cant back that up as I didn't go to school for economics lol. But even some academic Marxist economists fall for the bourgeoisie temptation of abandoning value.
Thanks for the comment! It's very frustrating when people call themselves "Marxist economists" and then throw out the most fundamental concepts. You have the "no bullshit" Marxists who try to erase dialectics. You have Keynesians or MMTers who stumble upon Marx's ideas and try to reinvent the wheel. In the most egregious cases you have people trying to reinvent the logic of Marxism with neoclassical concepts.
David Harvey is an interesting academic in that, from what I can gather, he seems to have imperialism flipped on its head - saying that its Global North workers who are actually exploited by the global South. WTF
And of course all of these so called "Marxists" wouldn't touch revolutionary practice with a ten foot pole.