What is the burden of explaining the delay in bringing a motion under Rule 24 and Rule 48?

I am mindful of the admonitions that the court should be primarily mindful of the rights of the litigants and not be penalized unduly for the conduct of their counsel: Habib v. Mucaj (2012 ONCA 880 (CanLII)). That directive is not to be taken as a license to ignore every instance of delay merely because a plaintiff may thereby deprived of a hearing on the merits. Conduct of counsel is seldom far from the list of items contributing to delay in motions under Rule 24 and Rule 48. However, the plaintiff in this case has utterly failed to discharge the burden of explaining (as opposed to merely cataloguing) the delay, has failed to demonstrate that inadvertence rather than indifferent commitment to the case was responsible for missing the deadline, has failed to show diligence in dealing with the action at any stage in the proceeding, but in particular in bringing this motion promptly and has failed to address or discharge the presumption of prejudice the lengthy delay in this case gives rise to.