It is good that they found a drug that helped.

Nothing is 100% "works for everybody". Including vaccines.

So it is good when treatment and prevention have multiple options of treatment. 

There are numerous anti viral drugs like ivermectin being explored for their efficacy. Some are showing promise.

The advantage ivermectin has over many of them is it not only is anti viral (the first 6-7 days of the disease) but is also anti inflammatory (when the remnants of the dead virus cause the so called cytokine storm). Ivermectin helps if taken very early or prior to infection by reducing the viral load, helping to prevent the virus from replicating. After the first week anti viral drugs seem to have little or no help (HCQ). Steroids taken early during the viral stage appear to be actually damaging. However once past the viral stage and where the body has started fighting the inflammation from the dead virus ivermectin helps by its anti inflammatory effects as do steroids. Inhaled steroids appear to be particularly effective in this later stage.

Ivermectin's anti-inflammatory characteristics appear to be what helps resolve "long hauler" symptoms. It has also showed promise in other viral diseases like Dengue, Zika virus and even gout. More tests are warranted.

That is my limited understanding of the mechanism.