You're right in that the "centralized single source of truth" actually rarely is a thing at scale.
It's common to adopt a mixed approach: some design tokens make sense to centralize (like global brand colors), and others are local, such as tokens for a specific product or sub-brand.
For example, a web app can build its own token architecture based on an existing foundation shared with iOS and Android apps. They share _some_ concerns, but technical implementations differ they may offer different theming features, too.
It's common to adopt a mixed approach: some design tokens make sense to centralize (like global brand colors), and others are local, such as tokens for a specific product or sub-brand.
For example, a web app can build its own token architecture based on an existing foundation shared with iOS and Android apps. They share _some_ concerns, but technical implementations differ they may offer different theming features, too.