Why is the "Secure Reply" button only available on already encrypted emails [Gmail]?

[Alexander Krivács Schrøder]

This is what I see on an encrypted e-mail sent to me:

And this is what I see on a regular e-mail sent to me:

The lack of a "secure reply" option on regular e-mails means that

1. I can't switch a conversation from unencrypted to encrypted easily, and
2. I can't respond with a "sign only" reply in an unencrypted conversation easily.

Is something wrong on my end or is this button missing on purpose?

[Alexander Krivács Schrøder]

How has this simple question/feature request not received any attention in over a year? I'm still having this issue. Can you either always show the secure reply button or have an option to always show the secure reply button? That'd be great.