I addressed this earlier, but one of the big things is that you can do these types of sets on multiple days. If i go and do a set of 2x20s at 90-92% i can repeat that anywhere from 3 to 5 days. That's a ton of training stress and adaptation. If i do 2x20s at 100% i can get one or two in before i need an easier day. The threshold work is nice, but it doesn't pay off the same as multiple days of sst. Now in the middle of the race season would i be wasting my time with 2x20s at 90-92%? nope, but in the middle of november when i'm not racing untill late feb or early march, they are very helpful in building power and endurance.

1 hour of sst in a row is nice, but often i can't do more than 2 of those back to back before i'm tired and need to swap to 2x30s or 2x20s