Monoclonal antibodies have to be administered in a clinical setting because they're administered by IV, but they also work best when administered early (diminishing returns after five days[0]), whereas most hospitalizations don't occur until the inflammatory phase of disease, in the second week. Remdesivir is/was the only antiviral being regularly given to patients with severe disease, probably out of a desire to ration it and only use it for people with the worst cases, but that's probably why it didn't really work very well, and is now mostly being abandoned[1].

The drugs that are most effective for hospitalized patients aren't antivirals, they're immune modulators: steroids like dexamethasone, and IL6 inhibitors like tocilizumab (which technically is a humanized monoclonal antibody, but not against COVID, and doesn't have any sort of antiviral mechanism of action).

[0] https://www.infectiousdiseaseadvisor.com/home/meetings/id-we... [1] https://www.healio.com/news/infectious-disease/20201120/who-...