People have a personal tipping point. They put up with tax and other deductions for a while, but the time comes when they hit the point and say sod it and start taking actions which ultimately reduce tax take, whether going part time, refusing promotions, taking early retirement, putting into pensions or emigrating.
Its classic behavioural pattern where you can put up with something but ultimately something will tip you over the edge, sometimes even the slightest thing. It’s not the last thing itself, it’s the cumulative effect.
Tax hikes also make people think - they look at their payslips more, they think of their tax demands more. People live busy lives and don’t really notice lots of small things but when they do notice, or see things on the media, it highlights the issue and triggers them to consider changes etc.
The clients I’ve had who have emigrated have never done it on a whim - it’s something they’ve been thinking of for years, but it’s often a relatively small thing that triggers them to actually do it.