It really isn’t an order to release 33,000 inmates, it is an order to reduce the population over the next 2 (or more) years. The real problem is that California has to release 33,000 more inmates over a short time than it sends to state prisons. (It is also a warning for other states since the ruling provides a basis for challenges to their prison crowding and treatment.) Half of the total to release is found in the short prison terms (often only 3 months) for parole violations. Reducing the population by about 500-600 a month meets the requirement.
One approach is that every month the CA district attorneys meet to decide which of the recently convicted felons will actually make it to the CA prison system. They are then forced to defend the convictions from their county as worthy of prison or trade current offenders for less serious prisoners. But each month they have to show a reduction in the total prison population.
There are a lot of other pieces to the solution relating to length of terms for some offenses, how some problems (e.g. drugs and addiction) are treated, and other ways for society to deal with certain crimes and offenders. But as long as voters require long prison terms without the same willingness to enact taxes to pay for these terms we will have a problem.