It’s not necessary, just cheaper. It also depends on what orbit you want the satellite to go to and what direction the coast is facing. The extra speed you get from spinning slightly faster at the equator than at 45 deg latitude is not significant (500mph vs 25,000mph). Inclination of the orbit is way more important, since Inclination changes are VERY VERY expensive. So if you are launching geostationary satellites, like DirecTV or some other regional capability, then you want very close to the equator. If you are launching an inclined orbit, like GPS or LEO satellites like Starlink, then you can choose a location that is close in latitude to the inclination you want to hit. Or you can choose a location that has a coastal direction that allows you to aim your rocket over water at the inclination angle you want to hit.
It’s not necessary, just cheaper. It also depends on what orbit you want the satellite to go to and what direction the coast is facing. The extra speed you get from spinning slightly faster at the equator than at 45 deg latitude is not significant (500mph vs 25,000mph). Inclination of the orbit is way more important, since Inclination changes are VERY VERY expensive. So if you are launching geostationary satellites, like DirecTV or some other regional capability, then you want very close to the equator. If you are launching an inclined orbit, like GPS or LEO satellites like Starlink, then you can choose a location that is close in latitude to the inclination you want to hit. Or you can choose a location that has a coastal direction that allows you to aim your rocket over water at the inclination angle you want to hit.