To complete what others have said about how it is taxed in various countries, in Spain the net profits you obtain at the end of the year are added to your income tax, which discourages betting if you are in the highest bands, 37% or 45% (in some regions a little more). The people who are in these bands either don't bet, or if they are poker or sports betting professionals they have long since emigrated, or they bet under the table, so to speak, in cryptocurrency casinos.
In most EU countries it's similar and you have to add the income from gambling to your total income on that year and pay tax. The only thing that differs between countries is the rate.
I agree that it should not be taxed, because whenever you take the risk and can lose everything, it's not a job or an investment. None of these give you 100% loss, unless you get scammed, but gambling does and therefore it should not be treated the same.
On the other hand, if they're taxing lottery wins, why not tax other forms of gambling? I'm still against it, but I know where this comes from.