They’ve been a “not user serviceable” component since before phones got water proofing.
Additionally plenty of things can be disassembled with screws and such, that are waterproof… Watches come to mind.
The fact that they’re making it impossible for we the people and owners of the products, to change the battery isn’t a technological limitation, nor a practical one. They did it so people will be forced to seek help to get a new battery, at which time, the vendor/carrier/whomever, can simply upsell the end user.
They did it to sell more phones. If you believe anything other than that, I have some land in Alaska to sell you.