Consider identifying an absolutely key subset of requirements for each position. Not the "wishlist" common in the advertised requirements, but the really non-negotiable firm requirements.
Then expand your recommendation submission to specifically ask the referrer to indicate for each requirement if it is met, eg:
(Make sure you are only asking legal questions - eg, work authorization is an allowed criteria because obtaining it for a worker is a very different and not necessarily even possible path, but many other things are specifically disallowed)
You could then have some form automation where if the answer to any of the above is "no" a text-box question asking for a free-form explanation of why the recommender feels the candidate is still qualified and suitable activates, and must be filled in before the form will submit itself.
Of course you also want to have a general space for custom text where the candidate's unique suitability can be explained - the actual "recommendation" vs "referral" part of the process as this will help distinguish the strong recommendations from the more ambivalent submissions.
No doubt some recommendations will still make dubious assessments, so it's probably worth having a feedback mechanism that serves as a reminder of how the recommendation system is supposed to be used.
The already raised idea of giving a non-specific category for social-obligation recommendations isn't a bad one, but probably needs to be vetted by legal for compliance with applicable regulations.
An entirely other tack is to have the recommendation form simply consist of a candidate name field and two upload widgets: the first for an actual letter of recommendation and the second for the resume. Some guiding text explaining the importance and expectations of the letter wouldn't be bad; regardless those who really understand what recommending someone for a position means and who take time to truly write a recommendation are going to be the inputs with weight distinguishing them from the convenience submissions.