Pending makes sense when the vendor is likely to meet the requirement but something is still in progress, like a renewal that has been applied for or a document that has been promised by a specific date. Rejecting a vendor in that situation creates extra work for everyone and can damage a relationship over a timing issue.
Rejection should be for cases where the vendor clearly does not meet a requirement and has no realistic path to meeting it soon. A pending status should always come with a date and a reminder, so pending does not quietly become permanent.