I doubt that the tax is the problem. I think people dont want to invest in Bitcoin because they do not understand what it is and how it works.
Some countries are not even strict yet with the earnings of the people related to crypto. Since they do not know how to recognize crypto yet, they just let it go that people are not declaring their taxes so I doubt as well that tax is one of the reasons. If you are earning from it then you still have an obligation anyway to pay taxes so for people not to invest in crypto just because they would pay taxes if they are investing in it seems not reasonable.
Lack of knowledge and lack of confidence are the main reasons behind this and that people still dont think so that crypto currencies can help them in having more earning.
All they know about the crypto currencies is that they are illegal and that investing into these coins will be a great loss and that they will not be able to make anything good. It will take some time to change the opinion of such persons and to understand this thing that investing in crypto will make them richer.
Media has a big influence on how the people perceive cryptocurrencies. Since the media is handled by big corporations, they can manipulate the minds of the people to think that cryptocurrency is bad. All I can see whenever I watch television and there is a bitcoin related report, they are focusing on scams. I believe that banks has something to do with it since they are anti-crypto. The lack of knowledge and trust are reasons why people do not want to invest or trade crypto. The lack of regulation to a certain country has a big weight as well.