Any of the following could be a driving factor in the decision to ignore non-vaccine treatments:
Money, both the NIH committee that sets treatment protocols and many in Congress have financial ties to the pharmaceuticals.
Inability to get Emergency Use Authorization for the covid vaccines if they acknowledged other treatments without going through the legislature and getting an exception to current law.
A belief that vaccines are the best way to go, as opposed to prophylactic treatments or treatments once a covid infection occurs.
A desire to get the new mRNA technology approved. It does appear to be a technology they can adapt quickly to any new virus. So could be beneficial in the future.