Inheritance taxes are trivial to circumvent with careful estate planning and vehicles such as trusts.
It's not clear that inheritance taxes are easier to circumvent than capital gains taxes, which certainly are easy to circumvent. Capital moves at the speed of light, to whichever locale offers the best return. The more you tighten your grip, Tarkin, the more numbered accounts will slip through your fingers. Investment is not like cigarettes; we don't actually want to tax it out of existence.
OTOH, old rich dudes die eventually no matter what. The death of a wealthy person would be a difficult event to conceal, even if potential heirs wanted to do so. At that point, Caesar can take his portion. Trusts etc. are fictional entities, created by the state. If there is some problem with these entities that prevents the levy of tax, the state may modify them to solve that problem.
I'm skeptical on how effective it is as a way of reducing taxes. Don't most countries tax you on residency anyways? And if you're physically in St. Kitts for 183 days a year, isn't it fair that you pay St Kitt's tax rates?