I know. If you inspect the GeneratePress logo on this site you will see it does have one as GP adds it by default. Why it is missing can be 1 of 3 things.
1. In Customizer > Site Identity – you do not have a Site Title.
2. A Plugin that is changing the markup – you have a lazy loader and a cache plugin that has added class attributes to the logo – so could be one of them
3. A Custom Function that is changing the markup.