On Android WhatsApp also requires access to all media files on the phone in order to use certain features that don't really need them, but that sound plausible.

For example, when you receive an audio message, if you want to listen to it, it will request full media access. Android apps can access media files they have created, so this permission isn't needed. But without granting media access (or tricking it into thinking it has it, like with GrapheneOS' storage scopes), WhatsApp won't let you listen to the audio. Same when trying to open an image full screen instead of just the in-chat preview.

If this were a small developer, I could assume it was done that way accidentally or to cut some corners. Coming from Meta, I can only assume malice.

A similar anti-pattern - WhatsApp has it's own contact list and list of users. However, you can't use it without granting the Contacts permissions. On my phone, though I have WhatsApp installed, I can't create a new chat - It just brings up the "Enable Contacts" dialogue. I can however use their web-client to initiate a chat, and when people can message me I can respond.