It's not taxes, the taxes are high but the gross salaries in EU and even in the UK are very low, compared to the USA. You don't have stuff like developer making 200K a year but taking home 50K a year, it's more like making 60K a year and taking home 40K.

IMHO it's the culture and the VC environment. There's simply not that much money around to throw at moonshot projects, therefore you don't have many unicorns that lose a few billion euros a year paying extravagant salaries for talent. Obviously EU is a very rich place but people with money invest their money in stuff that are profitable right away, likely to be profitable in short term because a giant company is behind it or invest in the US companies if they are more adventurous.

Taxes.

You are not getting that much in net salary above certain amount.

Europe is a hellhole if you are a young ambitious individual.