Im with you in that the freeway could be faster, but the drive down the backroads is quite nice. Almost all the lights on San Dieguito are green all the way to El Camino.
It’s more the matter of safety than speed. Bikes and scooters are dangerous. Your chance of getting killed per mile travelled on a motorcycle is 30 to 50 times higher than in a car. San Dieguito Road is scenic, but there are lots of hidden driveways where vehicles tend to appear without warning. If you’re not paying attention 100%, or if you’re driving too fast to stop in response to a careless truck driver pulling out of a driveway 200 feet ahead of you, it can end very badly.
And, when you’re commuting using the same road every day for months, it’s all too easy to stop paying attention or to add gas so you get home faster.