Provision of mentioning the choice of Reviewers perhaps assist the Editor-in-Chief or the Subject Editor to select the appropriate assessors & to respect the Author(s)' requests as well. But, I think they are not bound to that exactly.
I wanted to submit a paper for peer review online. I realised the journal requested me to submit the names of people i want to review the paper. I was flabbergasted. I declined to submit the paper.