Right now, the government has a simple story: essential businesses stay open, and everything else stays closed. It's quick to express and easily understandable.
But as soon as the government starts picking and choosing "nonessential" businesses to allow to open, every single nonessential business will be clamoring for an allowance and emboldened to present themselves as heroic frontline workers. You'll see every nail salon in the state market themselves as paragons of safety and virtue, professionally run, basically cleaner than the best medical facilities in the world. And if the government allows Tesla and refuses nail salons/meat packing facilities/hookah bars, you'll have a large constituency who'll be pushing duplicitous but superficially plausible arguments like "Newsom loves his BigTech buddies like Elon Musk but hates everyday regular businesses like Tyson."
The quarantine only has power so long as the public understands it and supports it, and the government has made the plausible assumption that picking and choosing nonessentials would undermine public understanding and enforcement of the quarantine more than the value that would come in allowing certain safe nonessential businesses to return to work.