I'm thinking it's because the phone is unlocked. I usually buy my phones from my carrier (T mobile) but this one, my note10+ I got directly from Samsung. My note 8 and s10+ both had video calling built in.
I'm late, however, I have Sprint and just upgraded from S7 to S8 and the apps I was introduced to which allows video calling is Duo. You may have to download that as it reads your address book and allows you to video conference just like the Iphone.