When the game initially loads, it reads all of the game files (which I know, because I have had many a crash at opening due to a tiny typo in one of these files). EB's game files are huge compared to vanilla. For an example, these are the...

export_descr_buildings:
Vanilla: 136,984 bytes
EB: 12,761,782 bytes

export_descr_character_traits:
Vanilla: 257,054 bytes
EB: 6,802,935 bytes

export_model_battle:
Vanilla: 189,717 bytes
EB: 691,852 bytes