Possibly a few of those had mechanicals. But its reasonably obvious that people where not seeding them selves appropriately. Finishing 5-10 minutes over 4 hours is justifiable. More than 30 minutes looks slightly bad and more than an hour is ridiculous, they never had a chance of finishing close to 4 hours.
In some respects perhaps the setup of the chutes promoted this. With five chutes (3-4 hours, 4-5, 5-6, 6-7 and +7) that where all about the same size, or say holding about 20% of 4000 people, roughly 700-800 riders in each. But only about 12 percent of the finishers actually got in under 4 hours. So a smaller 3-4 hour chute with some effort at policing the entry to it would be appropriate. Probably about half the size of this years chute.