Wealth storage
is a practical use case. This is a weird thing to grasp, but it's actually perfectly reasonable (I.e. utilitarian and stable) for an asset to be "purely monetized", in the sense that it has no value whatsoever except from its capacity to store value.
That said, you're right that ability to actually spend bitcoin probably shows up in any PDE that accurately models its market dynamics. If 90% of countries on earth ban bitcoin, and those bans are well-enforced, bitcoin probably won't be very valuable.
