No philosophical objection I’m aware of, just not prioritized yet, compared to other much needed work. Though, it is internally tracked that this is a much demanded feature. I’m aware that there was already a prototype for offline editing for mobile made.
Some hidden complexity:
Assume you have two offline phones, and edit an item I on device A, and device B. Then both devices come online and sync. Which version of I should be the one saved on the server? The one that syncs first? The one that syncs last? The one where the local device time at the time of editing was never? Should these be merged?
Of course, this is an edge case, and a default behavior would be much nicer than where we are currently at.