A mystery really. Loads of supposed "clinical trials" that turn out only to a have tiny numbers of participants, and no placebo group. Bigger trials (400 patients) that seen to show marginal effects like mild/moderate cases recovering a day or so earlier - particularly when it's used in conjunction with other drugs.
A couple that suggest some protection against progression to more serious disease, but when you look closer the trials don't have enough over 50s to get statistically valid data. The most dramatic trial included placebo group patients who went into hospital the day after the trial started - which is more like coincidence than evidence.
It's real enthusiasts recommend it as a preventative, taking it daily for months. Again there's a lot of anecdotal stuff on it working, but the enthusiasts are mostly young healthy adults, with an interest in health and nutrition. Again no blinded, randomised placebo group though. Just meta-analyses that compare them to groups that don't necessarily match them in terms of comorbidities or behaviours.
Personally, I don't know why people would want to take a drug daily, rather than have a vaccine. But then I don't take any drug daily, so maybe I'm the odd one.
There are some effects that on the face of it look worthy of a bigger (properly managed, broadly based, randomised, placebo controlled) trial of its use as part of a "covid lemsip" type approach for newly diagnosed patients. But so far the only trials that look like properly run drug trials have seen no statistically significant benefit. So it hasn't inspired anyone to go from hundreds of trialists to thousands.
TLDR
I have no idea why people want to take a random drug used off label without any proper evidence on efficacy.