SEOMatic using the pages title
Have you created a new SEOMatic Meta fieldType? 

I don't know whether there is another/better way of doing it, but what I do is create a new field of type SEOMatic Meta, then assign this field to the entry types of the pages you want the title to be made available to SEOMatic. There are all sorts of options within this field, but one of them allows you to select which field the title is pulled from.

More info on the SEOMatic Meta field can be found in the docs.