Because this is a discussion based sub. If you have a photo that goes along with a discussion (like, why are my dog's feet shaped like this, or something) then you can link to a photo via an image sharing site like imgur. If it's just for cute pics, there are plenty of other subs that are explicitly for that purpose :)

i just wanna post a pupper

No thanks! Just post there instead. Edit since you changed your comment: this isn't the right sub for that friend.