Why can’t I control volume across all of my Roku devices?

Hello, so I just have a simple question. 
Why is it that I cannot control the volume through the official Roku app across all of my Roku devices?

For clarification, I have 3 separate Roku devices in my home. Two Roku TVs, and a Roku streaming stick. I don’t know what series. The streaming stick is the issue. Now, it came with its own remote, and it controls volume just fine, working intended as a remote should. But the official app seems to be lacking this basic remote functionality. I fail to see how every other command for a remote can work from phone to streaming stick, but volume cannot.

I fail to see why I have to use a third party remote app to control the volume through my phone, when by all means the official app can manage this.

Needless to say, if you cannot implement such a basic function into your app, it leaves me to wonder how adequate your IT service is at managing more important tasks, such as protecting my payment information. I would like to see such a basic function that third party app developers are able to achieve, that somehow fail the people directly responsible for developing your official phone remote app.

Thank you, and have a good day.