Different countries, different rules when it comes to paying taxes. But it is also important to emphasize that paying taxes is a completely normal thing, especially if the tax money goes to the right purposes (public schools, kindergartens, hospitals, courts, etc.), and something else if it goes into the pockets of corrupt politicians and ordinary people only gets crumbs.

Your idea that crypto exchanges collect tax would be good for users, but the whole thing doesn't work that way. Governments want the tax to be reported and paid directly to them, not through some intermediaries like exchanges. The problem is in fact that taxes are too high when we consider the total amount we need to pay.

If we take the example that the capital gain tax rate is 20%, and you pay that every year it is maybe within some normal limits. But if you have VAT on every purchase which is again 20% or more you pay extra tax again on fiat you get from selling crypto. Although there are ways to avoid paying taxes when it comes to cryptocurrency, any trader on exchange which requires KYC will pay it sooner or later.