There is no option to extend or collapse all all the project/act lines on the Allocation Workbench, only one by one.
This is expected behaviour.
The Top Grid uses lazy loading to load the rows so it is technically not possible to load all rows.
Lazy loading (also known as asynchronous loading) is a design pattern commonly used in computer programming and mostly in web design and development to defer initialization of an object until the point at which it is needed. It can contribute to efficiency in the program's operation if properly and appropriately used. This makes it ideal in use cases where network content is accessed and initialization times are to be kept at a minimum.