Probably because it's hard to trust public health experts in a crisis whose very existence has already demonstrated a failure in their authority.

If I wanted to reduce the risk of acquiring or transmitting an airborne infection back in February, I would wear a mask and avoid enclosed spaces without waiting for CDC's permission. Indeed, I would ignore their advice to the contrary, which stood until April (!)

It would be really nice if we could defer to competent technocratic experts, but they earn their trust by having credible track records, not by collecting credentials.