Nubia is a clean and simple news or magazine WordPress theme. You love Minimalism, and you also love writing, nubia is designed for you. Maxima focus on showing your content in a clean and simple way, focus on images, typography, and white space.
The case for WordPress, for example, is that it’s loading some code that makes the score less, but if you checked the Bold for Ghost, you will get 91/97 score. So every time you install a new plugin to WP, performance will decrease due to the more resources loaded which are outside the theme scope.
One more important thing is that I optimize the demo images and I expect everyone should do this, but uploading big images would definitely make things worse even if the theme is 100% and Google would complain about images optimization as they play a huge role to the general score and considered outside the theme job scope. So I do my best from the theme side and then the site owner would do his best too.