Why do you need a premine, besides setting the price of the token?
Most cryptocurrency exchanges are corrupt, they don't care if the project is legal, ready or a scam, they don't go into the technical aspects of the new coin. In order to include a coin in the listing at an early stage of development, the exchange requires payment. It is on commissions, fees and the encouragement of the developers themselves that coins leave the premine.
Aside from the exchange listing fees, premine coins benefit both the developers and the project in many ways.
Some developers consider premine a coin to be a bonus for developing a project. Some use them to fund a project.
Where do the developers dispose of those coins that they received during the premine? Do they sell them?