Google’s official help page for Gmail attachments states that for personal Gmail accounts the sending limit is 25 MB. If your total attachment size is greater than the limit, Gmail automatically removes the attachment and adds it as a Google Drive link instead — which some recipients (and many automated intake systems) cannot open.
Work and school accounts differ: Google Workspace administrators set their own sending and receiving limits, so a file that sends fine from a personal account may bounce from a company one.
If you need the file to arrive as a true attachment rather than a Drive link, compressing it below the limit is the reliable fix.