Merit scholarships can be focused on several different things. We typically think of academic strength, leadership, etc as typical types, but there are also scholarships for other forms of top performing achievement/talent/interests- community service scholarships, some for the arts, some for certain demographics, etc. A family member of ours endowed a journalism scholarship at a highly regarded state university, so obviously that scholarship is targeted for a student majoring in journalism.
In some (several) cases a scholarship might say that priority is given to a student with financial need. IMO if you don’t complete the FAFSA or profile the school may then assume (probably rightly so) that you have no financial need. So it’s unlikely you are gaining anything by not submitting them.
And as has been mentioned, if some catastrophe befalls the family (heaven forbid) during your child’s years in college, schools can say they cannot assist you financially if they have no FAFSA/ profile form on file for you.