Because your applications used bitmaps for their interface, which now is not the most ideal thing to do.
How do you know what applications I run, and how they generate their user interfaces?
Or are you just trolling that “every Windows app ever written, except Dorico, is written incorrectly - and that’s why Microsoft doesn’t support Dorico without hitting this problem?”
It’s definitely something we will consider for the future. By no means simple to achieve, even with the icons/buttons etc. being drawn in a resolution-independent way, but I expect we will indeed tackle this at some point.
Thanks Daniel! 
Yes, I tried the developer’s suggestion. It didn’t work. Having been a part of software development teams for nearly 15 years, my (clearly isolated) opinion is that it’s not a reasonable solution. As was noted in my original post, I was already 4 hours in to this point. I installed and started using Finale in less than 10 minutes.
With respect to your other question, I’m not sure what you need to know in the Dorico forum. You insinuated that creating notation in Cubase via notation is even remotely useful. It’s not. If you want a word-for-word response, I was “disappointed with the results”. For further information, see “disaster”.
So you “fixed all your problems in 10 minutes” by uninstalling Dorico and installing Finale …
That was back in October 2017, but you are still here. Didn’t Finale turn out to be totally problem free either? 
I you responded that 1.5 years ago, the Dorico team could have helped you out more, and you could’ve helped them track and solve a potential bug.