Why not? Because you say so? Bitcoin seems to work as a long-term store of value very well so far.
I think Bitcoin makes Gold (as a money) obsolete.
Gold isn't money.
Gold was used as something to represent (back) money.
Gold is a store of value since it has had roughly the same barter value for the last 2000 years.
The deflationary nature of Bitcoin makes it seem that they are a nice way to store money, because there is a semi-limited supply of Gold, and Bitcoin are "mined"!
Since, there is nothing to "represent" Bitcoin other than fiat (and we're trying to avoid fiat right?), the only storage Bitcoin is is for ...Bitcoin.
The electronic nature makes it perfect for moving value.
To define something with ~3-year history suffering ~2000%+ volatility as "perfect store for value" is just downright funny.