It all seems fairly logical to me.
If you DNS becuase you are done for the whole event then OK bye. No problems, we’d rather you race but we can’t force you.
However if you DNS don’t come back tomorrow for another event, otherwise we will question what was wrong with the event you DNSed in, you have just “not tried” and that is against the rules. If you have a doctors note to explain thats fine though (this has been offered to the Algerian).
The difference between Ennis and this guy is that Ennis did her event and then withdrew from the next (for whatever reason, it doesn’t matter), the Algerian tried to hedge his bets and when he was doing better in one event he tried to get out of his obligation for the next. Nobody is stopping him withdrawing from all future events.
If he didn’t think he could do both events he shouldn’t have entered them.
There is also a touch of him being punished for being stupid and throwing his toys out of the pram. He obviously knew the rules or he wouldn’t have been at the start line. So why be a brat and do 100m and quit. Why not just jog round at the back of the heat and fail to qualify. Nobody would bat an eyelid and he would have probably done that much in training today anyway if he wasn’t entered into the event.