Because it's boring. It involves a lot of micromanagement to remember to spend the points to do it (much like with development and large nations in EU4), and it also means there is no underlying simulation system there to work with (i.e. natural development and culture change of pops depending on attacks on the province, being at peace, decisions, etc.)
It just makes it feel more like a board game or mobile game (spend mana to evolve your pop), rather than using the fact it's running on a full computer to provide a more interesting simulation.
It just makes it feel more like a board game or mobile game (spend mana to evolve your pop), rather than using the fact it's running on a full computer to provide a more interesting simulation.