Claiming that this is the reason is sort of like rearranging the chairs on the deck of the titanic when you can see the iceberg.
Much more likely it is to stop import/export to a competing app. The fact they will let you keep a local encrypted copy, but not an unencrypted one under any circumstances, is telling.
If we are to take the position that all users are tech literate and should be fully in charge of how their data is used, then even Cambridge analytica wasn't bad. People explicitly gave it access to data that was accessible to them. However, the uproar proves otherwise. People don't like it when they click yes yes and some random app has access to their social media data or messages. This is why Gmail also started requiring independent audit for all gmail apps.
SMS had the same problems forever, but isn't owned by a company, thus you can't blame xyz company if random apps access your SMS. No company got ever investigated by multiple nation states over that.
You still haven't addressed my main question though, how will a random app scraping your WhatsApp be any less of a scandal than Cambridge Analytica?
1. Shady addictive game requires full access to drive.
2. Shady game downloads all your chats with all contacts
3. FB is on fire since they allowed access to people's chats with others, even those who didn't download the game.
4. People get mad on FB/Google for not protecting their data.