>>8989094 (lb)
Because the symptoms are caused by our immune response to the invader, not by the invader itself.
The treatment aids the immune response by killing destroying the invader, in situ, resulting in the immune system having nothing to attack.
SNIP
Chloroquine inhibits the action of heme polymerase in malarial trophozoites, preventing the conversion of heme to hemazoin.11,15,16 Plasmodium species continue to accumulate toxic heme, killing the parasite.11
Chloroquine passively diffuses through cell membranes and into endosomes, lysosomes, and Golgi vesicles; where it becomes protonated, trapping the chloroquine in the organelle and raising the surrounding pH.10,13 The raised pH in endosomes, prevent virus particles from utilizing their activity for fusion and entry into the cell.14
Chloroquine does not affect the level of ACE2 expression on cell surfaces, but inhibits terminal glycosylation of ACE2, the receptor that SARS-CoV and SARS-CoV-2 target for cell entry.13,14 ACE2 that is not in the glycosylated state may less efficiently interact with the SARS-CoV-2 spike protein, further inhibiting viral entry.14
https://www.drugbank.ca/drugs/DB00608