I thought the EU was supposed to be all united and stuff. It's bizarre how different tax treatments are especially when people can just move.
If I had enough BTC I'd definitely relocate for as long as it took to pay the tax if I needed to cash out. If I'd held for less than a year I'd head to the Netherlands. The capital gains there is less than 2%.
EU is not supposed to be all united, well, apart from pro EU Federal State neoliberal corporatist's / bureaucrats kind of people's dreams.
European nations have their own long term traditions of law, economic policies, culture and so on and to compare the states of the US are, even if thought of as local law sandboxes, still very much bound by the Federal jurisdiction.
EU citizens in most EU countries are generally quite in much of opposition to generalizing everything for everyone as it tends to benefit only few economies while others suffer as the last recession clearly showed. Re-nationalization is a strong movement in last few years to counter idealism which has not translated into practice - Namely as cultures and economies within the regions are vastly different and have minds of their own.
Majority of the people can't "just move" apart from their holidays.
Most people are still tied to local employment and thus very immobile.
Other limiting factors are language and cultural barriers that prevent ordinary people to make a leap.
Even if you could remove 10-20 % of taxation in some cases, you'd had to uproot your entire life, learn new language, etc.
Conformism, nationalism, comfort zones... Many reasons pile up to make it a very different zone that say, the US is, where you could hop State very easily as an average citizen.
Netherlands would make sense for some as you are right for capital gains being very low, but for instance, I'd rather pay 20% to Spain than 2% to Netherlands for the sole reason of weather, language, culture, choice of different cities, local climates, people's outlook on life etc.
The problem with most tax residency laws is that you actually have to spend more than 6 months in a year to keep on enjoying (or not) those levels of taxation... Chancing tax residencies is not a quick process of packing your bags and going to another country as the laws are bit more persistent than just booking a flight and going - Freedom of travel is an amazing thing, but tax laws are very different thing.
I hope this made sense to you and you'll have a better idea why things are the way they are
