Elsevier provides a tracking system through which authors can see how many reviewers have been invited, how many have accepted to review the paper, and how many have completed the review. If more than two reviewers accept to review the paper or turn in their reports, it indicates the number of reviewers as 2+.
Editors might do their due diligence and invite more than two reviewers, i.e. 2+. A reviewer might accept to review, while after another 3 weeks to one month, the others might either have declined or not reacted to the email. In this case, the editor might have thought that after inviting three reviewers, for instance, it's time to wait for the completion of the review process. The problem now is that when the reviewer who accepts turns in their report, probably after 6–8 weeks from the date they accept to review, the editor might then realize that only one reviewer has accepted to review and then initiate another review process, inviting a minimum of one reviewer. Thus, the review process is done sequentially rather than in parallel, which elongates the review time.
Is it advisable to softly inform the editor after 3 weeks (if only 1 reviewer accepts to review) to invite more reviewers? How would one go about doing this politely?