Because it was vector-based, the UI could scale across different resolutions, though it was often noted for being particularly "friendly" to the 4:3 aspect ratios favored by competitive players.
This article dives deep into the history, functionality, and eventual replacement of Scaleform UI in CS:GO. scaleform ui csgo
While Scaleform was industry-standard for years, its implementation in CS:GO faced significant criticism: Because it was vector-based, the UI could scale