Think of it as I have two packs for levels.
Creek.level and roboplanet.level
Both use the cyborg enemies, by duplicating the cyborg enemy model and texture data across both files, Only the level file needs to be opened to get all nessecary data for a match.
Because modern OS will allow you to preallocate contiguous segments and have auto defrag, you can have it read this level file at max speed, rather than having to stop and seek to go find cyborg.model file because it was referenced by the spawn pool. Engine limitations may prevent other optimisations you think up as a thought exercise after reading this.
It's similar to how crash bandicoot packed their level data to handle the slow speed of the ps1 disc drive.
As to why they had a HDD optimisation in 2024... Shrugs