Besides population familiarity with material UI because of Google, am I missing something ?
Things I like about React semantic :
- very clean documentation : i can search, find , and tweek components
- Semantic is less opinionated visually than Material (IMO), and do appreciate lightweight.
Material design looks great by default but it infects the rest of your app really quickly since any custom components you build have to match it in visual style or it'll look really out of place. This was pretty hard for a small project without a designer.
Semantic basically looks like bootstrap without being bootstrap and is much easier to work with.
With bootstrap the basic buttons are fairly simple, so distinctive theming was easy, but with all the shadow and shimmer effects of the Material Design components its a lot of work if you want to change their structure to give it some of your own app's personality.
Also noting that the semantic UI docs still give a horrible mobile experience (iOS 11).