With a mecha show, ratings are secondary. What's most important is the sale of model kits, action figures, etc. If those are strong, then Sunrise could care less about ratings, because merch makes much more money anyway.
Then come DVD's. THEN ratings.
It sounds unusual, but it actually happens often. G Gundam, for example, is considered one of the most successful Gundam series, but its ratings were actually pretty low. Models sold like hotcakes, though, and continue to sell even today.