Because doing so will allow you to expand your horizons. In and around L.A. I would mix things up a bit. I would ride the Velodrome ( very exciting!). Sometimes just leaving the residence and riding in any direction - toward the beach to ride along the ocean or toward the foothills or even along the L.A. River on a dedicated bike-jog-walk path.
Then there'd be an occasion to leave the area completely. I'd drive down to San Diego or other communities out of town and ride at the destination. Also, depending on where on lives it may not always be safe to ride from the residence in a region deeply rooted in car culture with poor surrounding roads, expressways/highways until you move further away.
Yup, there'll always be brave souls but riding should not only be safe but fun! Hope my point-of-view helps.