Well, the email providers. And that could easily include Google without you even realising.
It's true that email isn't quite as insecure as it used to be (it was once compared to shouting your message at someone and expecting them to shout it in the right direction until it reached the intended recipient), but there are still many things missing compared to other forms of direct messaging, and there's good reason why many people and organisations don't want it used to send sensitive information.
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TLS just encrypts the IMAP / SMTP sessions, no guarantee it’s stored encrypted, let alone end to end
You didn't answer this question:
Well, the email providers. And that could easily include Google without you even realising.
It's true that email isn't quite as insecure as it used to be (it was once compared to shouting your message at someone and expecting them to shout it in the right direction until it reached the intended recipient), but there are still many things missing compared to other forms of direct messaging, and there's good reason why many people and organisations don't want it used to send sensitive information.
How is that different from your browser and the bank website being able to read the same PDF transmitted through the website?