You're taxed when you earn the money already. Taxing again at the point you deploy it is double taxation. Many countries don't tax capital gains at all because

You're taxed when you earn the money already. Taxing again at the point you deploy it is double taxation. Many countries don't tax capital gains at all because of this fact. Moreover, you want people to deploy their capital in the economy. Hiking taxes on capital gains would massively disincentivize people. Unlike other taxes, capital deployment is a risk based economic activity: if you raise taxes, people will be less inclined to invest it on risky ventures as opposed to keeping it in very safe assets (e.g. bank accounts or real estate).