Like most everything else the Governing Body does, this is likely motivated by concern over legal liability, especially for schools that are directly sponsored by the Organization. They don't want to be seen having any direct legal connection to local congregations so they can't and won't enforce anything at the local level. But their own schools are a different matter.
They can't get successfully sued if they pushed the official narrative and standard of care with respect to the vaccines. They do not, however, actually care about the health (physical or spiritual) of the Elders or members of local congregations unless it can impact them legally or, more precisely, financially.