iOS/iPadOS is fundamentally a mobile operating system - optimised for low power operation - and technically, this has potential implications for some USB accessories/storage devices. Some USB storage is better suited for use with mobile OSs than others. Some storage devices, such as high-volume SSDs, are completely usable with iPadOS - but require some care with how they are used with iPad.
iPadOS assumes that external storage immediately writes to non-volatile storage. It is write-caching, employed by some high capacity SSD storage devices, that can cause corruption of the SSD filesystem if the drive is disconnected from the iPad before data has been saved to non-volatile storage.
To cite an example, a traditional spinning internal HDD (as found within many older desktop computers) will suffer corruption if power is removed from the computer (or if the HDD os simply disconnected) prior to performing an orderly shutdown. While this is a loose analogy, it broadly illustrates what will happen when some types of SSD are simply disconnected from an iPad.
Write-caching cannot be directly circumvented by the iPad Operating System; for those storage devices that don't immediately write to non-volatile storage, safe dismount is possible - however, it is currently necessary to perform a clean shutdown of the iPad to achieve this. As for why Apple have not provided method by which the User may signal an intended device disconnection, to devices that employ write-caching, is known only to Apple's development team.
Apple does invite submission of constructive comments and feature requests via its Product Feedback portal. If you would like to see additional features or specific functionality in a future version of iPadOS, this would be the most appropriate channel through which to make your voice heard:
Feedback - iPad - Apple
