In a sewing needle tip, as we know, the surface area is less. Hence the pressure exerted will be more. Greater the surface area, lesser the pressure and lesser the surface area, greater the pressure. So, as the surface area is very little, the pressure exerted will be more. Or we can say

The tip is sharp it can penetrate the fabric easily by applying more pressure on the fabric but if it is not pointed then more force is required to penetrate the fabric as the pressure on the fabric will be less.