Looks to me like this behavior has been set by Apple. After tests and searching it appears as though the keyboard will only show up if a user event occurs.
With that being said you may have to force a user event to allow this. This means making a start button, on a click, on an agreement, etc.
Here is an example that can get you started. If this isn't an option you might have to either rethink your design or do some deep digging and hope there is a solution out there somewhere.
Good luck.