For the projects that require more complex design in terms of number of sections and variety of templates it's very limiting to fit into 60 fields.
To illustrate: project consider multiple brands, blog articles are written for all of them. Blog articles are grouped into several topics and have different desig templates (for example article about working hours has different template compared to the new product promotion or collection promotion). Since the order of custom fields can't be changed to accomodate different sections in a template it's challenging to fit into 60 custom fields for several design templates.