Default removed "firmware" files in z1c-44-uk.system.flashable.zip?

i'm currently trying to make a flashable zip with my "own" firmware "D5503_14.3.A.0.681_EURO LTE"

when i compared the the content of systems.tgz from the file z1c-44-uk.system.flashable.zip with the system.sin file of my firmware i noticed a bunch of files are missing in the tgz file.
so i looked at D5503_14.3.A.0.681_Generic UK.ftf and noticed the firmware files are there.

Different files in system
D5503_14.3.A.0.681_EURO LTE vs 1c-44-uk.system.flashable.zip


D5503_14.3.A.0.681_EURO LTE vs D5503_14.3.A.0.681_Generic UK.ftf


D5503_14.3.A.0.681_Generic UK vs 1c-44-uk.system.flashable.zip


why were these files removed in the flashable zip?
Phones: Sony Xperia Z1C, Xiaomi MI2
Tablet: Sony Tablet S 3G
Retired: Meizu MX M032, Sony Xperia Pro, Samsung Galaxy S+, HTC Desire Z, Motorola Milestone, HTC Hero.