Direct in-vehicle access to data basically means that any third-party service provider would have direct and full access to the data inside a (running) motor vehicle in an uncontrolled way.
However, directly providing such access to in-vehicle data poses serious security and safety risks to the vehicle, you as a driver and your fellow passengers. For example, direct third-party access to vehicle functions can facilitate hacker attacks, since every new external data interface increases the number of potential targets and entry points.
To limit such risks, a better and more balanced alternative to direct in-vehicle data access is off-board access. It allows manufacturers to communicate the relevant vehicle data in a secure manner to an external server, from where third parties can access it.