In my opinion, the key difference here is that it would be extremely difficult for a large percentage of the worlds cash holders to not spend any cash, whereas it would be possible for a large percentage of bitcoin holders to not spend bitcoin. The average cash savings rate in the US averages around 5.7% (https://ycharts.com/indicators/personal_saving_rate), and even in extreme cases it's rare for the savings rate to exceed 80%. In contrast, I would think that over 10% of bitcoins in circulation may be held long term for investment purposes.

Saving bitcoin isn't 'anti-bitcoin' but at the same time liquidity is a key feature required by currency.