When every sale happens in one country, VAT is a single rate applied to a price. Sell across borders and the question changes from "what is the rate" to "which country's rules apply, and why." A German garden centre buying from an Italian grower, a Dutch wholesaler reselling into France, a private buyer ordering a single olive tree from abroad — each is a different tax event, even for the same plant at the same price.
Three things decide the answer: who the buyer is (a VAT-registered business or a private consumer), where they are (inside the same country, elsewhere in the EU, or outside it entirely), and where the goods physically go. Change any one and the correct treatment can flip from standard-rated, to zero-rated with the buyer accounting for the tax, to no EU VAT at all.
Get it wrong in the cautious direction and you charge tax a customer should never have paid, then spend a quarter unwinding it. Get it wrong the other way and you have under-declared — a liability that surfaces at audit, with interest attached. Both are a records problem.