[msutherl]

This is speculative, but Max/MSP 5 – which was a very dated piece of software at the time – was re-written using JUCE for the UI, and IIRC JUCE wasn't music-focused at the time. Quite likely the current music focus has everything to do with Cycling '74 making that choice, the subsequent advent of Max4Live (which popularized Max), and the dominance of that kind of rounded-corners, pre-flat design aesthetic so common in music software since Ableton Live took over the world, which happens to be JUCE's default style.

[FigBug]

JUCE has always been music focused. Originally it was created at the same time as the DAW Tracktion. It was split out of Tracktion and become its own product and Tracktion was sold to Mackie. Roli ended up purchasing JUCE and Tracktion was spun off into its own company.

Source: Tracktion developer since 2005.

[msutherl]

Ah, thanks for the clarification! Turns out I could have discovered that if I had Googled: https://www.juce.com/history-and-development – so much for speculation.