The big problem is the buying anything with it.
If you could buy stuff with it and it wasn't an absolute headache (install app, pay transaction fees) and it was easier, it would be more popular.
That would also remove the "it's a speculative asset bubble" problem.
For the interim, using it as a private bank, assuming you can cache it out at an exchange for local legal tender, is the next best thing.
The only true way to make it a currency is for it to have its own country - bunch of people somewhere decide to use it for all their stuff, trade goods and services. Problem with that OFC is a lack of free land and energy.
So maybe when we live in space, and need a long term store of value, but don't really want to carry around bars of gold or platinum, it can have some serious uses. Until them it is exactly like buying oil - technically asset trading but really hard to realize the value in any meaningful way.