This is by design. Access requests with multiple items will be broken out into individual operations for the backend to process.
The reason for this is that approval processes for access items can have different approval chains and timelines, and we were seeing issues with large access requests having to wait for all approvals for all items to complete before the items were provisioned. This is how it works right now, but it may be improved in the future to allow more control over how these items are processed.