so, i take from your reply...
1. the scale... are you saying the number of cases is a consideration?
2. the effect... are you saying the impact to the economy, in that it would produce undue economic hardship, is a consideration along with the scale?
1) They didn't know enough about it.
2) Yeah, one case in the entire country would have been seen as an extreme and ridiculous overreaction by the public in this state. Especially with the POTUS telling the public it was all under control and there was nothing to worry about.
3. The shut down would be severely harmful to the state's economy, workers, and businesses, and it would be doing so in the blind, considering at the time there was no known help in sight from the federal govt.
Understand, the shut down in California came within 48 hours of Trump declaring a national emergency.