Do you have comments turned ON in your settings? Look at SETTINGS>DISCUSSION in your dashboard.
I have set default at “allow people to post comments on new articles” ???
As well as other comment settings as well
Maybe you have some settings in your theme to hide/show comments?
Also keep in mind that these settings in discussion applies to new posts, not already posted. For those you have to bulk edit and allow comments.
Also check if you set that login is required for post comment.
