Because VAT is regressive. Also, if it were set high enough to collect an entire state's revenue then it would be evaded on a spectacular scale: it's a tax on m

Because VAT is regressive. Also, if it were set high enough to collect an entire state's revenue then it would be evaded on a spectacular scale: it's a tax on movable goods, many of which can be bought elsewhere in the EU and imported, let alone the possibilities of simply cheating on your return. The rates of excise taxes on cigarettes and alcohol in the UK are essentially maximised due to evasion already, for example. If you do want One Tax To Rule Them All, the most likely options are either some kind of land tax (because land doesn't move and can be confiscated in lieu of payment) or various kinds of Pigouvian taxes on fixed industrial polluters.