External docs solutions, or docs solutions that aren't designed for developers, tend to create silos. When information is siloed like this it often gets forgotten or goes stale.
With Tech Docs, the opposite happens. Your internal docs are centralized and live alongside all the important metadata in your service catalog, like ownership, dependencies, or Service Maturity level. Tech Docs are easily discoverable and searchable by all developers. Tech Docs are more visible to the entire organization, and so better updated and maintained.