Why does my Xbox Captures take as much as a lot storage on a USB drive in comparison with OneDrive

I’m not an knowledgeable on these things however for some motive my Xbox captures take up a lot storage when uploaded to a USB drive in comparison with after I uploaded them to OneDrive. I wish to save all my captures earlier than they get deleted, however I don’t wish to pay cash for additional OneDrive storage, so I’ve been making an attempt to add them to USB drives however they take up an excessive amount of house on the drive. Thanks for all assist!