That is one of the problems when it's a publicity stunt rather than a formal Royal tour @ThePoshUns - there's a certain amount of background work, but not to the same level (it also, of course, depends on co-operation of the principals).
It's also being shown at the moment with multiple questions online about the suitability of the youth charity they went to visit - there are commentators pointing out that several of their staff have been involved in public support of Hamas on multiple occasions. Again, unwise, the sort of thing that would have been checked out for any official visit - and probably not something that the Sussexes would have considered in advance.