Most peoples right now using bitcoin as investment. Its happen because many government still prohibit and ban bitcoin if used for payment. Because of that reason, many peoples and investment firm using bitcoin as an investment
Other than government bans, I think that people use bitcoin as an investment because of the lack of adoption. For now, theres not much areas where you can use bitcoin. There are even some countries where bitcoin is not accepted as a payment system so I dont see the point of using it as a medium. Also, fees are high so its not that favorable to use btc. Its much more profitable to have bitcoin as an investment instead. Its possible that btc as a medium will be more possible in the future.