You have 2 curse setup, so it's:
A - You need to have an item, passive skill or ascendancy that enables you to curse with more than one curse - if not your Projectile Weakness is overriding Poachers Mark (you should notice knockback). To confirm, try to reverse curse gems in you setup - place Poachers Mark under Projectile Weakness then you should get charges, but wont have Projectile Weakness applied
B - Poachers Mark has only 20~30% chance to grant charges on kill, so you should notice it on every fifth~third kill, but still getting none would be highly unlikely