And because the tax years don't line up, it's more costly than filing just in the US, or just in the EU, plus if you moved with a company and were granted RSU's

And because the tax years don't line up, it's more costly than filing just in the US, or just in the EU, plus if you moved with a company and were granted RSU's in the US, or keep property or assets in the US ... it's just a pain to calculate properly. Have friends who regularly spend 10x more than I do my accountant for my tax return because of this.