Main reason is if you use Bitcoin to buy something today you lose chance for that Bitcoin to be worth much more in future. It is smarter to spend regular money which loses value over time and save your Bitcoin which could gain value. This will likely remain case until Bitcoin price becomes more stable and it is used as legal currency in many places. Until then most people will see it as long term investment not as something to use for daily shopping.
This is also one of the reasons why some people avoid using Bitcoin for everyday transactions, and we know that Bitcoin is the best asset with the potential to achieve financial freedom when used for long-term investment. Furthermore, what are the regulations in each country? If Bitcoin were banned as a legal means of transaction, engaging in such activity would be illegal, leading to much greater problems, which is why people avoid it. Bitcoin is indeed a much better long-term investment because this asset has advantages that can lead to maximum profits.