I'm pretty sure that the second reason is the only one. ;PTrel
I’m pretty sure that the 8806 was chosen for two reasons. ...One is thickness....
...The second reason is cost...
If I remember correctly (I don't have my notes handy) the 8900 in the Planet Ocean is almost identical, in diameter and thickness, to the Rolex 3235. That would mean the thickness endemic to Omega's watches in recent years has been entirely a design choice rather than a restriction. (Those clear casebacks they love to use definitely don't help.)
My point being, though, with regards to this No-Date NTDT Bond is that the choice of the 8806 vs the 8400 means that users get the choice of a great feature or no features at all. Neither movement has a date feature that could be damaged.