There are a few reasons for this, here's the two main ones. Honda is very sensitive about mpg averaged over their whole fleet for CAFE qualifications and so forth. When you have your lights on it actually reduces your mpg by about a 1/10th mpg as the engine has to work slightly harder turning the extra load on the generator/altenator. I also learned Honda only charges the battery during decceleration, apparently they've been doing this for the past 15 years, pretty smart. The other reason is DRLs have never been proven to make a difference as a safety feature.