Drills such as hubud are just that, drills. They are designed to teach certain tactics for dealing with a particular angle at a particular range, and if done with proper intent and playing the drill true, they can be great teaching/learning aids for developing mechanics and attributes.
Hubud, like knife tapping, is about being behind in timing (otherwise, why would you be reacting to a strike from your opponent at that range?), and unfortunately, most places that I have seen teach the drill never even mention that aspect, let alone emphasize it in training, therefore the person who is being attacked is moving at the same time as the person doing the attacking. Combine that with a bunch of repetitions that are static in nature and intent, and you end up with a dead drill that does not lead to learning or the development of the attributes that it was designed to. Another problem that shows up regularly is if the timing is actually emphasized, a person's ego is often such that they get competitive and start trying to win the drill rather than playing it true (I think most have fallen into this at one time or another, myself included).
Yet another issue is that often, the person feeding fails to give a realistic attack. This is a common issue in FMA in all sorts of drills, not just hubud. If a strike is not coming in on a realistic angle and actually targeting you, it is very hard to work the mechanics and tactics that a drill is designed to teach. I see this all the time with knife tapping and with other drills, even with the long weapon. Sometimes this is intentional, as in the attacker changing the angle of their attack in an effort to win the drill and not get countered, and sometimes it is not, but the result is the same in that you end up with a meaningless drill that might look good at seminars, but has no chance of actually conveying the information it was designed to.
If taught and practiced properly, hubud should then eventually be taken out of the drill and practiced in a more random sequence, and then eventually in complete free flow/sparring.