The feature is meant for especially sensitive documents, you wouldn’t want it turned on for everything in the organization because it limits useful features like search and printing. More mature products like Azure Information Protection let you require encryption for certain documents based on policy, but that doesn’t seem to be part of what Google is announcing here.
> you wouldn’t want it turned on for everything in the organization because it limits useful features like search and printing
Some organizations would want to prioritize encryption over search/printing. (Also, there's no reason search and printing couldn't work with encryption.)
It's more of an issue that people have to interact with vendors outside their direct ecosystem, who maintain different email systems. I can have all the PKI infrastructure I want, if my contracting officer has to coordinate payment of a $10M or $100M deliverable with a foreign company with different laws around encryption, I may have no choice but to send some things unencrypted until we can mutually agree on certain processes.
At the very least, I can confirm that ProtonMail and Apple's Mail clients let you search through the message contents of encrypted email. I'm sure there's a performance hit, and admins wouldn't be able to search through the encrypted emails of their Workspace users, but that's a much more reasonable tradeoff.
I'd be interested to know the implementation... Most search-over-encrypted-documents implementations either don't scale well (eg. require the client to do all the indexing and upload the encrypted index), or have reduced privacy (allowing the server to infer which words are in which document).
Admins of many orgs don't like letting the user have options for things like security.