It's easy to pontificate after the event, Snowball, from the comfort of your armchair with the benefit of a few hours to mull over all the alternatives. The race umpire John Garrett had no such luxury and had to make a decision immediately, bearing in mind the rules governing the event.
The situation arose because of the utter stupidity of Mr Trenton Oldfield who was lucky enough (thanks to the diligence of the assistant umpire) to escape serious injury or death. The rules provide for a restart, which umpire Garrett decided should take place. Then, far from an oar “coming off” the Oxford boat, it was broken in a collision caused (as decided by the umpire and confirmed by the TV replays) by the aggressive steering on the part of the Oxford coxswain, Ms Zoe de Toledo. Finally, the Oxford bow man almost certainly suffered exhaustion due to the break in activity (again down to Mr Oldfield).
So yes, not a very satisfactory end to a popular event, but all credit to Oxford for their sportsmanship in completing the race. But that’s what happens when people behave with less sense than they were born with.