While you don't have to report that you failed to calculate a hash, it matters that, had you succeeded, you would have reported it. Someone who calculates hashes with no ability to report them shouldn't count as a participant.

To put it another way: if there is a group of participants with spotty Internet that, after succeeding in calculating a hash, have only 10% chance of actually reporting it, then working backwards, we need to divide by .1 (multiply by 10) to calculate the number of participants. But if they have a 0% chance of reporting success, then we'd have to divide by zero. This is because they aren't actually participants. It's attempting to count non-participants.