Its not low taxes that motivate extra immigration.
But its lower taxes then your neighboring regions that give your extra immigration and also an extra boost of happiness for the poeple (morale and loyalty).
If the other lords around you have 17%, you can have 16 or 15% and already more people will move in.
While it makes perfect sense, that's not actually true. At least not yet.
Morale, loyalty, and food are the main things you need to keep high. Low taxes will result in higher morale and loyalty, but they do not
directly influence peasant migration.
