a) The debtors tend to suck since they are new.
b) The judges tend to just be randoms or not high quality (ie some are just random parents who volunteer who may not have actually debated) so they don't have the ability to parse through what actually happened during the debate properly.
When you get better, you have to learn what arguments matter and don't matter. The skill part of debate is knowing how to throw away as much useless arguments as possible and argume defensively and offensively against the parts that do matter.
You do not have to bother with any of the opposing sides arguments if you have concluded they are pieces of trash. I myself have won debates just by proving in 10 seconds that 4 minutes of the opposing teams arguments was irrelevant and just moved on.
Sheer volume is a valid tactic, since the opposing team COULD drop important arguments that actually matter, so that's part of the skill. I've watched plenty of top level debates where people talk both fast and slow.
Nobody wins just by being fast.