iPhone and iPad message storage different

Hi,

I would like to understand why my gf iPad with only 32gb have like 10gb of messages data while her iPhone with 64gb have around 500mo of message data.

I would like to lower the amount of data on the iPad since it’s 32gb and full but I don’t want to delete important stuff that should normally be on my 2tb iCloud.

So why is the message data on both linked device isn’t the same and how to get rid of the 10gb of pictures/video without deleting them forever.

BTW message are kept for a year in settings

Thank you