1) People will be more mentally prepared for stricter measures down the line
2) You are reducing the rate of infection. Every little bit helps
3) You cannot turn off the whole economy at once. Chaos would ensue. You turn off things little by little and, if necessary, you keep the essential. But finding that balance isn't easy and may require some degree of trial and error.
Take the examples of China. Grocery stores are working, but slower and few hours. Delivery guys absolutely must work, and they do it with increased protection, etc... They probably didn't found that balance overnight.
Education, an investment for the future, is one of the least important economic sectors for the immediate short-term (save for it's function in guarding children while the family works). Kids are resistant but will be very likely be found to be capable of transmitting infection... It's a great place to start.