It seems most Zcash users are not interested in its privacy features, but hope to profit from other people's interest in its privacy features.
It's also possible they give up because many wallet don't support privacy feature or found out it took some time to create transaction. Even after few major performance improvement, it took 19 seconds to create transaction with 1 input/2 output on Raspberry Pi 3[1].
[1]
https://garethtdavies.com/crypto/zcash-shielded-transactions-on-the-raspberry-pi.html