I know several people that got cleaned out in IPOs partially due to how taxes work on no-liquidity (lockout) periods. If you IPO'd at $10 ($3 goes to the tax man), and when you can finally sell it 6mo later and stock is only worth about $3, the IRS makes more money than you.
Checkout what happened at Uber [0].
My cousin at Aurora borrowed money for his tax bill on IPO. I don't know the final numbers, but I hope he at least broke even.
Remember London and Amsterdam have extremely strong finance industry lobbying, and that shows up in their lawmaking.