The beach is symbolic. People are objecting to the lack of objectivity which went into making the decision to keep the beaches closed beyond the time when government scientists reported the half-life of the virus was very small in high-temperature and humidity environments. Add the breeze which is almost always present at the beach, and the fact a very high number of the infections were transmitted indoors, and healthy people who are not at risk pushed back against the lack of science and common sense displayed in maintaining closure of the beaches.
What people are most upset about is being unable to return to work and having their jobs, or the businesses they own be declared as non-essential beyond a point where it is quite clear the hospitals will not be overwhelmed. People know hospitals are not even close to capacity and are losing money. They know doctors and nurses have been furloughed from hospitals. People are upset they did what they were asked to avert a crisis in hospital care, and now they are being asked to continue to miss paychecks until there isn't a single death in the county in which they reside for 14 days straight. The "no deaths for 14 days straight" was an invention of Governor Newsom, and was never recommended by anyone at the CDC, or by doctors Fauci and Birx.
One of our basic rights is the pursuit of happiness. It uncertain times, or in times of great danger people are willing to set it aside. Times are more certain now, and the great danger in California never materialized.