If you carry (give or take) 1 TB of data with you, a seed phrase is about 0.000000001% of that. I can think of so many ways to just hide a few bytes in that mountain of data, that it would take a very long time to find if you don't know where to look.
I guess they have some sort of software that scans for specific types of files. I believe any .gpg, .txt, .asc, .exe file would be more suspicious than a .jpg or .png. I mean, obviously, you can find places to hide your data. Nobody would ever try to manually check 1TB of data. At the same time, automatically scanning using software is faster (good for them) but has security holes (good for the people who want to hide sensitive information)