Because we haven't got much more promotion or marketing to make it popular on bitcoin as cash . There are only people in bitcoin community to use it as cash. However, bitcoin is not still accepted from the government so that everybody is disquiet and do not get bitcoin as cash.
- Bitcoin is not ran by some company so there is no one who want to spend from their own pocket in marketing/promotion of bitcoin.
- There are also many miners, node hosters except bitcoin users who are supporting bitcoin network and make sure it keep running.
- Sooner or later more and more people will start using bitcoin as cash and for this bitcoin doesn't need to be accepted by government.
Agreed, if bitcoin already set by the government, all will again question about the matter of taxes and fees. But the effect is whether it can make people feel more comfortable to invest in bitcoin?