They are probably asking for your ID as a way to speed up the process. They will usually ask "have you sent money before?" as their way of verifying if you are already in their system. When you say "yes" they know you are in their database, and then ask for your ID just to verify that the info they have in the system is correct.
Keep in mind, you will not be able to receive a refund - if needed - if you do not have an ID matching the "sender info" that was supplied. And now, more than ever, refunds are becoming necessary when using WU/MG due to receivers being "flagged" (denied) due to suspicious activity. WU/MG receivers have become a magnet for scrutiny due to goverment pressures for cracking down on suspicious looking (multiple) transactions.
I never had a problem with WU/MG for years, and now have had 2 or 3 "issues" in the last year.
Also, FWIW, you are on camera at almost every WU/MG location, with rare exception.