I guess the questions are:
... why the captain felt inclined not to report it (e.g. was he worried about the punishment he might receive if he reported it, or did he have a goal fixation of 'getting the flight under way' etc etc?);
... if the first officer raised objection to not reporting it, and if not, why not;
... why the wheel ended up off the hard surface.
I believe the first and second question are potentially just as important as the third, if not more so.