Google said this is because they want to get advertisers up and running faster with these dynamic search ads. Google said, "to get your DSA campaigns up and running more quickly, AdWords will now automatically use the "Recommended bid" when you select a category during the creation process."
The example Google gave was if you have four categories selected: "sandals", "running shoes", "loafers", and "flip flops"” you no longer have to manually set bids for each one. You can also adjust recommended bids or leave the field empty to use the ad group's default bid.
Forum discussion at Google+.